If we drew an imaginary line straight down the middle of the human body, it would look pretty similar on each side.

We see this kind of symmetry in lots of animals, from cats and birds to worms and frogs. In fact, about 99 percent of animals have bilateral or two-sided symmetry, says my friend Erica Crespi, a WSU biologist. See Crespi’s full answer on the Dr. Universe website.