Kage-e was commonly used to entertain guests at parties during 19th century Japan. The pictures are comprised of two parts: a silhouette image (viewed first) that resembles an easily identifiable object, and a real image (viewed second) that reveals the silhouettes true identity.

For example, what appear to be silhouettes of three swimming goldfish (above), is actually two flying Tanukis , one of which is crushing a hunter with its gargantuan testicles (Seen below).

Via: Pink Tentacle