Some games/pranks to play on a stoned person to trip them out?

The question says it all. I have a lot of stoner friends and I know a few pranks to play on them to trip them out such as "you're running through the forest, you're running through the forest, you're running through the forest, you hit a tree." and "you're in the box." but thats the problem... those are the only ones I know. so I'm looking for some more games or pranks to play on them to make them trip out. I find their reactions extemely funny ("take me out of the box! Please!") haha. Help, please? :3