(CNN) -- Antoinette Tuff's knees tremble as she stares at the black barrel of an AK-47. Her hands shake so much she can't hold a pencil.
Facing her, a stocky young man dressed in black points the assault rifle at her.
"This is not a joke," the man shouts at Tuff. "I need you to understand this is not a joke. I am here. This is real. We are all going to die today."
Tuff, a school bookkeeper, isn't supposed to be at work today. She's filling in for the front office receptionist as a favor. Now she is the only one standing between the gunman and 800 children at an elementary school just outside Atlanta.
Tuff began her day by reading Psalms 23: "Yea, though I walk through the valley of the shadow of death, I will fear no evil."
As she watches the gunman raise his rifle to fire, Tuff realizes she is no longer just sitting in a school. She is in the valley of death.
Tuff was too terrified to speak when the gunman burst into the school, but what she said during the standoff that followed was credited with saving hundreds of lives. Tuff recounts the standoff in her new book, "Prepared for a Purpose," in which she attributes her actions to God. Yet Tuff's story can also be read as a survival guide for anyone who wonders what to do if they're suddenly facing someone with a gun.
We asked survival experts to analyze Tuff's actions, and they freeze-framed three subtle moments in which her deft maneuvering increased her chances for survival. To Tuff, these actions seemed insignificant at the time. But they went beyond her celebrated ability to build empathy with the gunman by disclosing her personal struggles. Tuff instinctively took a series of actions that professionals who deal with violence take years to master, experts say.
"She had a unique, deep and profound skill set that she was able to bring to the situation," says Kris Wilder, a 30-year veteran of the martial arts and author of "How to Win a Fight: A Guide to Avoiding and Surviving Violence."
"She played her part perfectly."
Tuff says today that she didn't have time to think -- she just reacted. But talk to her and it's easy to see why she connected with the gunman. She is a jovial, unpretentious woman with a husky laugh; after five minutes you feel like you're talking to your favorite aunt. She is now touring the country, giving inspirational speeches.
"I just try to help people with their purpose," Tuff says. "What do you do when God calls your number? Are you ready?"
Here are the three moments that show why Tuff was ready:
Moment 1: She "changed the channel"
Tuff watches as the gunman lowers the rifle and paces across the front office. He is a stocky man in his 20s with brown, cropped hair and a nose that looks like it's been broken. He is breathing heavily as he turns to Tuff and bellows:
"Call 911 and call a news station. Tell them I'm going to start shooting."
Tuff's shaking hand grips the phone as she dials 911. She quickly complies with everything the gunman asks, addressing him as "sir" as she relays his messages to the dispatcher. The minutes drag on, and the gunman shouts threats and waves his rifle at Tuff.
Tuff takes a risk. She asks the gunman an odd question:
"Can I go to the bathroom?"
The gunman stops pacing. He turns in her direction. The angry expression on his face evaporates.
Tuff's odd question "changed the channel," Wilder says. He and other survival experts say gunmen often whip themselves into a state of rage before they shoot people. They are literally no longer thinking straight -- the "lizard brain," or the brain's lower functions, are in control. They often refuse to make eye contact with their victims and back up when they are about to shoot.
Tuff noticed that the gunman refused to make eye contact with her. Be wary when an angry gunman refuses to look at you, says Laurence Gonzales, author of "Deep Survival," a book that examines why some people are more resilient facing sudden life-threatening situations.
"He's got himself into a fit of rage and he's trying to protect his emotional state," Gonzales says of Tuff's gunman. "He knows it's a very fragile state. If he doesn't make eye contact, he can keep that emotional state encapsulated."
A potential victim can sometimes break that murderous mood with an out-of-the blue question that forces a gunman to think.
"The guy is locked in and he's going to continue on his path unless there is something that changes the channel," Wilder says of the gunman Tuff faced.
Wilder saw another woman skillfully execute Tuff's maneuver in a less lethal situation. Wilder was riding a bus one day when he saw an enraged man hop on board. The man appeared to be high, his jacket was bloody, and he looked like he wanted to hurt someone. He started messing with passengers, trying to start a fight, when he came upon a young woman eating pretzels.
As he approached the woman, she did something that stopped him.
"You want a pretzel?" she asked.
The man halted, confused, and then muttered, "Yes."
"Open your mouth," the woman said.
He did as commanded. The woman plopped a pretzel in the man's mouth. End of story. The man didn't bother anyone else because she had changed his channel, or shifted his thought patterns.
Tuff threw a pretzel question at the gunman, but at the time she thought she made a terrible mistake.
"It was almost ridiculous that in the middle of a violent standoff I asked the gunman if I could go to the bathroom," Tuff wrote in "Prepared for a Purpose," which was co-written by Alex Tresniowski. "If I had heard someone else did that I might have thought, 'How dumb can you be?' "
But Tuff was actually being clever, Wilder says. Changing the mood can work in all sorts of potentially violent situations. Say you're facing a gunman who wants to rob you -- or worse, someone who is preparing to shoot you -- and your only chance might be to make a run for safety.
Change the channel with an out-of-the-blue question like, "What time is it?" or a nonsensical question like, "What was Gandhi's batting average?" A question that shifts the gunman's thinking may save your life, Wilder says.
Wilder says words are weapons, and he keeps a mental list of nonsensical questions -- Where did you buy that shirt? Did you get Lasik surgery? -- that he can fire off at a moment's notice.
"All my go-to questions are all chambered," Wilder says.
Moment 2: She anchored herself
Tuff's legs wobble as she rises to go to the bathroom. But before she can take another step, an awful thought comes to her: If I go to the bathroom, the gunman might follow and I will inadvertently lead him to the classrooms where the children are hiding.
By now Tuff knows the whole school has been warned over the school intercom that there is an intruder in the building. The teachers are keeping the children hidden in the classrooms.
Tuff watches as the gunman takes a plastic chair from the office and uses it to prop open the school's main door. He raises his rifle and begins shooting at police, who by now have gathered outside.
Glass shatters and bullet casings scatter across the office. But for some reason, a blanket of calm settles over Tuff. She watches the gunman fire away, but doesn't move from her seat.
Tuff takes another chance.
"Sweetheart, come back in here," she tells the gunman. "Bullets don't have no names. And those bullets gonna kill me and you. I need you to come back in here and it's gonna be you and me and we will work this thing out."
Press accounts of the standoff made much of Tuff's ability to empathize with the gunman. She called him "sweetheart," told him about her marital problems, and revealed that she had once contemplated suicide.
Tuff's book reveals that her struggles went even deeper. She says she moved 14 times in one year as a child, was homeless at one point and contemplated suicide on four occasions.
But here's the thing about empathy: It matters little if you're not calm enough to employ it during a life-threatening situation, survival experts say.
Professional snipers take years to train themselves to be calm while stalking a target, Wilder says. They get into a virtual hypnotic state where they slow their breathing and turn off their emotions while preparing to shoot.
"They go into a zone," he says.
Tuff and the entire school staff had received some training for dealing with dangerous situations involving trespassers. But it was life's hardships that had conditioned her like a soldier. She automatically calmed down when faced with an extreme situation. She had been trained to do so by her own struggles, as well as by her faith.
Tuff calls it "anchoring." It's the spiritual practice she incorporated into her life that she says helped her during the standoff.
She goes to sleep every night with an audiobook of the Bible playing softly by her bed to instill a sense of peace. At 5 each morning she listens to gospel songs, talks out loud to God and reads the Bible. She ends her anchoring practice by sitting in silence for 15 minutes, waiting to hear God.
"Trust me, sitting for 15 minutes isn't as easy as it sounds," she says in "Prepared for a Purpose." "I could sit and watch a TV show for an hour, but listening for the Lord for 15 minutes was a challenge. I had to work on it. I had to practice."
Tuff wasn't just a receptionist when the gunman entered the office. She was like a finely tuned spiritual athlete. She was ready.
That's what quick-thinking people who survive life-threatening situations often do: They practice calmness before their crisis, says Gonzales, author of "Deep Survival."
You don't have to open the Bible to practice calmness; you can do it during rush hour, he says.
"You have to practice emotional calm in your everyday life to have it in an emergency," Gonzales says. "Look at your emotional responses to everyday things: If you're stuck in traffic, are you pounding the steering wheel or do you turn on classical music and relax?"
Tuff's calmness -- not just her empathy -- helped her connect with the gunman because emotions are like viruses; what you feel can be transmitted to others, he says.
"If you're with someone who is lighthearted and happy, you're going to feel the same emotions," he says. "She transmitted these feelings from her own deep beliefs and sincerity, and he caught this emotional message from her. It completely disabled him."
Tuff didn't know she was so poised during the standoff.
"I thought I was screaming," she says today. "I didn't realize how calm I was. I went back to listen to the (911) tape and it was like I didn't even recognize who I was. I could not repeat what I said if you asked me. I had no idea what I was saying. I know it was God."
Moment 3: She evoked the motherhood mystique
The gunman obeys Tuff's commands and wobbles back into the office. He slumps in a chair. He's bleeding from his elbow; he cut himself while shooting at the police.
"I feel so badly about my life," the gunman says softly. He tells her he is off of his medication for a mental disorder; that he should have gone to the hospital.
"Well don't feel bad baby," Tuff says. "My husband just left me after 33 years. I mean I'm sitting here with you and talking about it."
Tuff tells the gunman she can let police know that he didn't harm her. She offers to walk outside with him so they won't harm him.
They talk more, and she negotiates his surrender with the 911 dispatcher as the gunman lies on the floor and places his rifle on a counter.
"I really messed up," the gunman tells Tuff as he waits for the police to enter the office.
"It's going to be all right sweetie," Tuff tells him. "I just want you to know I love you, OK, and I am proud of you. That's a good thing you've given up, and don't worry about it. We all go through something in life."
It's a peculiar pattern you read about in books on war. When soldiers are dying on the battlefield, some of them will cry out for their mother with their last breath. The mother is a figure of immense primordial power for men, and Tuff used that to her advantage, Wilder says.
Listen to the 911 tape to see how she managed the transition. At the beginning of the tape, she is not the mother. She is a soldier obeying a superior officer, barking out his orders to the 911 dispatcher. By the end of the call, though, she is cooing "sweetie" and "baby" to the gunman as if she is a proud mother.
Tuff is indeed the mother of two grown children. In much of her book, she talks about the way she pushed her son, who is disabled, to care for himself as much as possible, and encouraged her daughter to excel in school. The tough, nurturing habits of a concerned mother pervade her being.
Becoming a maternal figure to the gunman helped save Tuff's life, Wilder says.
Up until age 7, mothers are the provider of everything to boys, Wilder says. A gunman pumped up on adrenaline and anger is often functioning at the mental state of a young boy -- they see the world through simple emotions like hate and fear.
A woman who can appear as a maternal figure to a gunman in such a frenzied state can reach him in a way no others can, says Wilder, who also owns and teaches at the West Seattle Karate Academy in Washington state.
"She had life experience," Wilder says. "She was coming from that mother archetype. That would not have worked if she was a first-year teacher out of Missouri State."
Can a man facing a gunman somehow become a paternal figure and talk him down from his rage? Not likely, Wilder says. He says male hostage negotiators train for years to reach gunmen, and they sometimes fail.
"It's really easy for another man to kill another man," Wilder says.
Tuff's standoff ended when she negotiated the gunman's surrender with police. No one was hurt. The gunman was later identified as Michael Brandon Hill, who was charged with aggravated assault on a police officer, terroristic threats and possession of a firearm by a convicted felon. A spokeswoman for the DeKalb County public defender's office says a motion stating that Hill is incompetent to stand trial has been filed, and his case is still pending. Tuff says she has not spoken with Hill since their encounter.
But she has spoken many times about her experience, and has been flooded with letters and gifts from strangers. She says it was no accident that she was in the front office that day.
"I know that every last thing I've gone through, from childhood up to the end, prepared me to save that young man and all of those students," she says.
Still, there's a harsh truth that cannot go unmentioned in stories similar to Tuff's.
An extraordinary person like Tuff can do everything right in such a situation and still get killed, says Gonzales, author of "Deep Survival." He cited the Columbine shootings, where, apocryphal or not, one victim of the notorious Colorado high school massacre was said to have evoked her Christian faith before she was killed by one of the teenage gunmen.
"She could have easily done what she did and got herself killed," Gonzales says of Tuff. "She was very lucky in addition to being very brave."
Luck, it has been said, is the residue of skill. And Tuff's skill offers a lesson for others who may wonder how they would react in a similar situation.
Tuff was a shape-shifter during her faceoff with the gunman. She started off as his victim, then turned herself into his messenger, confidant, protector and mother before reverting to what she was all along:
What would you have done if you were in Tuff's place? Share your thoughts in the comments below.