Kage-e ("shadow pictures") -- a popular form of Edo-period woodblock print -- were appreciated by children and adults and commonly used as party gags. These pictures consist of two parts: a "shadow" image and a "real" image. The shadow image, which typically bears the shape of a common, easily identifiable object, is viewed first. The real image, viewed second, reveals the surprising true identity of the shadow.

Here's a nice example by ukiyoe master Kuniyoshi (ca. 1852). It shows what appear to be the silhouettes of goldfish...

But look again...

It's a flying tanuki crushing a hunter under the weight of its mammoth testicles.

Here are a few more kage-e by Hiroshige (ca. 1842). The shadows cast on shoji doors belong to men in interesting poses.



Pine tree



Uguisu (Japanese bush warbler) on a plum branch



Salt-dried fish



Kettle



Hawk



Stone lantern



Goose on a rock

[Related: Joge-e: Two-way pictures]