Here's one I got a freind of mine with a few week's ago.
First get a 2 liter of coke and some mentos.Tie a string around the mentos.Put in right near the top of the bottle of coke then put the lid on it.Cut the string off at the bottom of the lid til you can't see the string but the mentos is still there.Then just leave it sitting there and wait for one of them to open it and then prepare to laugh your head off.
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