The pupils of the eye can be circular, or linear (either horizontal or vertical).
Predators have vertical slits, herd creatures have horizontal slits. I don't know what this means, or how it may relate to other body parts or character in general, other than those with tall, flat heads, tend to be more aggressive e.g. tyrannasaurus rex.
Not all animals have circular pupils. Some have slits or ovals which may be oriented vertically, as in crocodiles, vipers, cats and foxes, or horizontally as in some rays, flying frogs, mongooses and artiodactyls such as sheep, elk, red deer, reindeer and hippopotamus, as well as the domestic horse