It's where they all lie down and pretend to be asleep, and the person who's "on" walks around going "ah-aah-aaaah-boo" or whatever and trying to make them move. If they get seen moving then they're "on".
Basicly sunbathing, in other words!

Jaccairn, I hope you do well, and are healthy! Good luck. I'd echo Katcal, be careful.

Hex, I'm sorry for your troubles. Hopefully his parents won't be too hard on him. . . #crosses fingers#