How do you make a half-filled cup of water full without actually pouring? (video)

Here's a fun party trick. Fill a plastic cup halfway with water and ask guests how to make the cup full without pouring. They might try thinking of other ways to get more water into the cup without having to pour, when they should actually be thinking of how to shrink the cup down to size.

Here's the simple stunt in action:

Front page thumbnail image: Al.geba /