Now, you could take it one step further and fill them with different things, so the poor sucker you pulled it on would have even more work ahead of them seperating them.
Jello in some, water in others, sand in still others, hmmmmm, what else could go into a foam cup
I was thinking to make it even funnier . . . make it so when you first walk in there's only a few cups scattered in the first room then make it get more and more dense as you go back in the house. Every corner you turn would get worse and worse - LOL
Another fun cup trick is to fill a glass full of water and have someone place their hands palm down on a desk with fingers on top of the other fingers. Tell them it is a test of balance and place the full glass on top of their hands. Once they have it balanced simply walk away, they are then stuck with a full cup of water and no way to pick it up!
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Sometimes, when i'm lonely... i crawl into a laundry basket and tickle my ears. But, Some times I don't...