The idea was born out of boredom, after a sweaty Saturday game of Frisbee at University of South Florida on March 31.

Freshmen Anthony Shortt, Sarah Claussen and two friends would construct what they called bottle rockets out of plastic soda bottles, water and dry ice. They'd take them out to the grassy quad, cap them, and watch the carbon dioxide pressure build and pop the bottle, to produce a loud boom.

The first boom that day was louder than they expected. It resounded off the walls of the residence halls surrounding the quad.

The second bottle was taking its time. The girls got bored and went inside. Anthony Shortt and his friend stayed outside, babysitting the second bottle so passers-by wouldn't get scared by the boom or walk too close.

As they waited, police arrived, asking questions.

"I made it," Shortt said.

Out came the handcuffs.

From the dorms, Sarah Claussen watched her boyfriend get cuffed and ran outside.

"I was with him," she said. She was cuffed, too.

Shortt tried to explain that water rockets are noisy, but not dangerous, that not even the grass underneath was hurt.

Police called them dry ice bombs and charged both students with detonating a destructive device, a third-degree felony punishable by up to five years in prison.

Claussen's mom bailed them out of jail the next day for $2,000 each. That night in the dorms, they received an eviction letter and were told they couldn't step foot on campus until an emergency hearing a week later.

Shortt is an architecture major with a 3.2 GPA. Claussen is an aspiring journalist who got straight A's last semester. That week, Claussen lost points in her gerontology class for not attending. Shortt got a zero on an oral presentation he wasn't allowed to give.

After the hearing, they learned they could never live on campus again.

"We understand we made a mistake," Claussen said. "What we did was not going to hurt anybody."

Opinions differ on whether a dry-ice device could cause have caused destruction.

Gary Ensmenger, who sells water rocket kits to teachers on his Web site h2orocket.com, said that given enough space, the rockets are harmless.

"Basically, it's just water and air," Ensmenger said. "There are a lot ways of making a soda bottle explode.''

Dr. Jason T. Spratt, associate dean of students, said dry ice bombs are considered either injurious or disruptive behavior. "It may not have harmed somebody,'' he said, "but it could have."

Shortt is living in an off-campus apartment. Now, he's a year behind on his degree.

Claussen fears for her future. "I just hope that the court does not decide to take away my youth for a dumb stunt I pulled as a freshman," she said.

The state attorney's office has not yet decided whether to prosecute the case.