WARNING: this is a "jumper". Do not watch with elderly relatives. Do not watch if you have a heart condition. Do not watch if you do not appreciate "jumpers". Just in case you're not sure what a jumper is, this vid has a sudden surprise that might make you jump. [just so I won't get moaned at, & it's only posted because I thought this 1 was better than most]
http://www.metacafe.com/watch/790504/girl_scare_prank/