Here's one;
Loop some string around your victim's key, place the key in a glass of water. Put the glass of water containing the key into a freezer, leave it overnight. In the morning leave your victim a note giving them a clue as to where their key is, when they find it they should find their key encased in a block of ice, in a glass, with some string hanging out the top.
Loop some string around your victim's key, place the key in a glass of water. Put the glass of water containing the key into a freezer, leave it overnight. In the morning leave your victim a note giving them a clue as to where their key is, when they find it they should find their key encased in a block of ice, in a glass, with some string hanging out the top.