Smears

 Smears, Multiples and Other Animation Gimmicks

 "In live-action films, motion blurs are natural occurrences. In animation, you have to make them from scratch. And most of them are pieces of art by themselves."
-Michael J. Ruocco animationsmears.tumblr.com

Amazingly smears and multiples are even utilized in Stop motion animation:

Armikrog