Looking around to cheat on an exam so that your head and neck resemble a periscope. Your head swivels back and forth so quickly that even the dumbest teacher will probably catch you. However, there is always the chance that periscoping works, and it's one of the best feelings in the world. It's commonly used by those too lazy to put any effort into cheating discretely.
John: Dude that test was hard
Fred: Hell yeah, luckily I was able to cheat off the smart kid next to me
John: Ya I could see you cheating from across the room. You looked like a periscope!
Fred: Lol well at least Mr. Walters didn't see! He's oblivious!