The flashbang went off with a deafening BOOM, and green smoke began to waft through the air. Bystanders yelled for help as emergency responders rushed to the scene, walkie-talkies crackling.

There wasn't actually a terrorist attack in the Lowcountry on Thursday morning - it was all just a drill, but what if it weren't?

That's why more than 20 public safety organizations, hospitals and local and state government agencies joined forces for an annual emergency response exercise. This year, instead of a natural disaster, the focus was a terrorism incident reminiscent of last year's Boston Marathon bombings.

"Obviously, with recent events that have occurred in the United States over the last decade, decade and a half, we feel it's important to prepare for all hazards in Charleston County," said Jason Patno, director of the Charleston County Emergency Management Department. "Just as we have prepared this year for our annual hurricane season ... we wanted to reinforce the training of our staff by adding a terrorism scenario to the exercise."

The drill's scenario involved two "explosions" - in Mount Pleasant and James Island - at a made-up cycling race in the Charleston area. Some emergency responders arrived on scene, while others directed efforts from Charleston County Emergency Operations Center in Ladson.

Lt. Chris Brokaw of the Charleston County Sheriff's Office said these drills are an opportunity for multiple agencies to practice working together, which is what they'd do in a real crisis situation.

"We learn where our weaknesses are, where our strengths are and what we need to work on. It's exercises like this that you can't get in the classroom or by watching videos," Brokaw said. "That's the best way for us to learn and to protect the public, which is the whole purpose."

To prevent a real version of Thursday's staged scenario, Patno said residents should employ the "See something, say something" philosophy.

"If you see something that looks suspicious, report that to local law enforcement so they can investigate the matter, and they'll determine whether or not it's an actual item of concern," he said. "Don't be afraid to report something to the authorities."