Slow-motion water balloon face explosion
Things are always cooler when slowed down, just ask John Woo. In that vein, check out this cool but also very funny video of a rather unfortunate chap being hit full in the face with a water balloon.
This type of slow motion effect is achieved when each film frame is captured at a rate much faster than it will be played back, so when replayed at normal speed, time appears to be moving more slowly. The technical term for slow motion is overcranking which refers to the concept of cranking a handcranked camera at a faster rate than normal (ie faster than 24 frames per second).