The sound of metal hitting the floor echoed through the hallways of the childless elementary school. It was an empty clip from a gun, fallen to the ground.
"That sound should be imprinted in your brain," Zach Hudson, co-founder of Defensive Tactics Solutions, told the educators in the audience. "That is the sound of survival. That is the sound of opportunity."
That, Hudson said, is the best time to attack a shooter if one enters the school or classroom.
On a recent Saturday in Lake Mary, Fla., Hudson and his partner, Mike Friedman, conducted a free active shooter self-defense workshop for teachers and school staff members.
Since the deadly school shootings in Newtown, Conn., last year, school security plans have included arming teachers, adding police officers and armed security guards, changing how schools are designed and adding bulletproof backpacks and whiteboards to schools.
In the new school year, some educators are taking it upon themselves to be prepared for the unthinkable.
The self-defense trainers, both parents, believe that workshops like this one should be mandatory for educators.
"You got to make sure you get those fire drills in every year," said Hudson, who was a CNN Hero in 2012 for his work with senior citizens. "Fire drills are important, don't get me wrong, but guess what, kids aren't dying in fires. They're dying because they are being shot. That's the truth, and that's the threat."
They passed out a pocket-sized active shooter reference guide published by the FBI that says people have three options when an active shooter enters a location: run, hide or fight.
"Fight as a last resort and only when your life is in imminent danger," it says.
This course offered guidance on how to escape or take cover but focused most of its four hours on how to fight and disarm an attacker -- something few educators have ever considered how to do.
"It's very sad that we have to go through this kind of training to know how to protect our kids," said Marsha Taylor, a teacher of 25 years who works with young children.
The protection exercises started with a fake gun pointed at the educators. "It takes the fear out of it," Hudson said.
Participants were taught how to grab the barrel and point it away while holding the slide so the handgun cannot fire. Parts of the workshop were similar to a self-defense classes, where participants learned how and where to hit and the best position to stand when approaching an attacker.
"You have eight weapons," Friedman told the class. "Two hands, two elbows, two knees, two feet."
The educators of all ages practiced how to use those body parts on pads held by the instructors; they were encouraged to make every strike fueled with aggression and anger.
"We don't need to be armed with a weapon -- a gun per se," said Frank Taylor, a day-care owner who took the class. "But if we have knowledge of how to use our bodies and our surroundings, than that in itself is the best form of arming ourselves."
The tactics and strategies were tailored toward a school setting, instructors said, and part of the workshop focused on the school and classroom setup. Teachers were told which ordinary items found in a classroom might be used as weapons -- for example, throwing a stapler at the shooter or using it to hit an attacker in the temple. If scissors were available, educators were told to aim for the eyes.
"Who cares how you incapacitate?" Friedman said. "Just attack the attacker. That's the mind set."
In the school's hallway, educators got a detailed lesson in how to run from the sound of bullets.
"'Cover' means that whatever you are behind will stop a bullet," Hudson explained, urging them to run from cover to cover.
When told to hide, Hudson reminded the group that if they aren't seen, they're less likely to be shot.
The workshop ended with a "bad guy" with a gun entering the classroom. The educators were taught how to find the room's "blind spot": a place where they won't be seen when the shooter entered the room. It was also the best position, the trainer said, to use the element of surprise if they needed to disarm the shooter.
A shooter, of course, that these educators wanted to prepare for but never hope to encounter.
"In addition to us providing exceptional education for the students, first and foremost, they have to be protected," Taylor said. "If they're not safe, then it doesn't matter what we do from an educational standpoint."