Hop David's "Rams".
The pattern repeats by rotating; the sheep are turned upside down-- to make the repeating pattern that fits together neatly. It is a "Rotation" ("Turn", "Spin") type of tessellation. Also notice that the actual tessellation part isn't a perfect picture of a ram-- the rams' rear legs are too long. However, by letting the shape change slowly from left to right, Hop David makes the pattern look wonderfully realistic at the extreme right and left sides. This kind of slow transition is called a "Morph". Some morphs have one shape on the left or at the top-- let's say, "swans" for example, and a completely different shape on the right or at the bottom-- let's say, a fish. Can you find a morph in M. C. Escher's work? Escher did many of them.