Flash mobs can be lots of fun and the craze is growing.
For the uninitiated, a flash mob is a group of people who plan to descend on a store, shopping mall or other public place with an impromptu song and/ or dance.
Phoenix attorney Ruth Carter says if you're planning a flash mob, you might want to check with a legal representative to make sure that what you have planned doesn't put you on the wrong side of the law.
A trespassing charge or injury to a stranger often become possibilities in flash mob gatherings.
Carter is a flash mob fan herself. She joined her first one in 2009 -- the "Drop Your Pants" mob on the Valley Metro light rail.
"I went and rode the light rail in my underwear with about 90 other people," Carter said. "That was the first time I did a flash mob, and I fell in love with them instantly."
Now she plans flash mobs with a group called ImprovAz. She's even written a book called "Flash Mob Law: The Legal Side of Planning and Participating in Pillow Fights, No-Pant Rides, and Other Shenanigans."
Carter said that a lot of things can go wrong with flash mobs.
"If you're being active, you might be at risk for committing assault or some kind of trespassing, depending on where you are," she explained.
She said her group always looks at the possible legal implications before it plans a flash mob.
"For every event," she went on, "we look at what we think we want to do, and react with, 'What might we be accused of doing wrong and what might we actually be doing wrong?'"
Carter said checking with your attorney before you plan a flash mob could, indeed, save you from getting into trouble.