Jumpscares

Jump scare (plural: jump scares) (narratology) The technique, typically used in horror films and video games, of having something occur suddenly and without warning to frighten the audience. (Wikipedia)

Screamer(plural: screamers) A Flash program or video that appears to be a game, a test or a still image. The point is to get somebody to concentrate on the program for a period of time and then all of a sudden a loud scream is heard. Often these screams are coupled with a scary image. These programs are meant to be jokes to scare the hell out of people. (Urban Dictonary)