This is one of Escher's tesselating fishes in 3D. Several of these fishes can be grouped together, so that they form a never ending pattern. See also: http://www.quirxi.net/misc/lizard_tutorial/index.html.
This is a mold pattern for a single 12mm roundball bullet. This kind of typically cast in lead and used for slingshot shooting. The model is hollow inside and has two drains, which makes printing a bit cheaper. But you will have to close the openings before using it.