this is a cheap trick to fright your friends.
Step 1: You Need:
You need a rubber band and two pieces of wire.
Step 2: Bend the Wires
first bend the two wires like the ones in the picture
Step 3: Wrap the Rubber Band
wrap the rubber band round the wires
Step 4: Finish
now wind up the rubber band and place the springer under a book, under a iPod, ...
when your friend pick up the book (iPod, ...) the springer spring around.