by Sarah S.
This nicely creative tessellation shows translational (slide) symmetry.
The "tile" (tile = repeating shape) is very neatly, precisely reproduced and fits with all the other tiles perfectly, without gaps or overlaps. That's what a proper tessellation does.
Sarah uses the motif of a monster to get away with explaining the odd outline. This is actually a good thing, and very popular with tessellation artists. Hop David, one of the best tessellation artists alive, has done a few monster tessellations. I've also written a short, funny essay about why monsters make a good theme for a tessellation.