A gunman is loose. His shots echo in the building. People scream and fall.

Now, say police, is a good time to act less like a human and more like a dog. Move — quickly.

You don’t see a dog standing around when danger presents itself, said Marietta Police Lt. Jake King. A dog, he said, has one of two responses — fight or flight.

“We can learn something from our dogs,” said King, addressing about 600 people Sunday afternoon at Marietta Middle School.

That lesson: Do something. Avoid the shooter. Deny him the chance to kill you. If you must, defend yourself; you’ll probably save some lives in the process.

For the second time in less than a month, Marietta police hosted CRASE — Civilian Response to an Active Shooter Event. As in the first, Sunday’s seminar left few seats vacant as people took advice on what to do if they’re confronted with armed mayhem.

The session featured slides, as well as film clips from classes about how to deal with an active shooter. It also showcased snippets of 911 calls, including a fragment from a mass shooting that stands as one of the nation’s pre-eminent armed disasters: the 1999 shootings at Columbine (Colo.) High School.

That clip, played near the beginning of the 90-minute seminar, showcased the natural human responses to stress — denial, followed by a horrified recognition that something is dreadfully wrong.

“There is a student here with a gun,” says the 911 caller, who identifies herself as a Columbine teacher. “He has shot out a window.” Moments later, she realizes everyone is in danger: “Heads down under the tables!”’ she yells to her students.

And then, a heartbeat or so later, her words tumble over themselves in one long, hysterical sentence. And two armed teens are still shooting.

“The best thing you can do is move — move as fast as you can,” King said. “Hiding and hoping will not work.”

‘Everyday events’

Marietta police already had planned an active-shooter seminar when an armed couple killed 14 people in San Bernardino, Calif., earlier this month. That tragedy, an act of terrorism, led to an overflow crowd at Marietta High School’s auditorium for the first seminar. It also prompted officials to schedule a second session.

The San Bernardino shootings stirred Maurice and Tama Colson of Atlanta to bring their daughter, plus three of her friends, to the second seminar.

Tama Colson has family in San Bernardino. “That hit close to home,” she said.

Maurice Colson nodded. “These are everyday events,” he said. “They are tragic.”

Active-shooting events have increased 500 percent in the past five years, police say. They don’t see that easing any time soon.

King was succinct. Marietta, with its schools, shopping centers and office buildings, could be an easy target.

“Do we all agree that this trend is not going to end unless we do something about it?” he asked.

Yes, the crowd answered

‘Waiting to be shot’

Consider the passengers on United Airlines flight No. 93, the doomed airplane that crashed in the Pennsylvania countryside on 9/11. The people on that plane, said Marietta Police Lt. Brian Marshall, weren’t willing to sit while terrorists hijacked the plane. They attacked their abductors — and, most likely, changed the way people react to hijackings.

Since then, said Marshall, several would-be hijackers have faced passengers ready to fight to save their lives. And so it should when an active shooter tries to kill, he said.

Marshall paused while a quick clip depicted a fictitious shooter, walking through a warehouse. One warehouseman slips away. He tries a door; it’s locked. He looks for a weapon. There; a fire extinguisher. He slips it from the wall and waits. When the gunman rounds the corner, the warehouse worker sprays it in the man’s face. The man falls. His gun clatters to the floor.

“That’s better than waiting to be shot,” he said. “Eventually, these guys (shooters) will get the hint” if people fight back.

Fighting back is something Ben Henderson knows well. Fifty years ago, he was a door gunner on U.S. Army helicopters in Vietnam. He came to the seminar with his wife, Doris Henderson.

“I want her to know more about this,” he said.

Doris Henderson agreed. “These days and times, it’s a scary situation,” she said.

Hannah and Corey Hall want to be ready, too. Each has a permit to carry a weapon.

“I figure we’d learn something new to protect ourselves,” Corey Hall said.

“The more I can know,” said his wife, “the better.”