A lot of animals, anything from a house cat to
tigers, lions, jaguars, and leopards, have vertical slit pupils that appear to
be up and down. Their pupils, when constricted, (get smaller) become round.

These animals are all predators, or hunters. The
eyes of predators, including humans, can focus rapidly. Their pupils contract
and dilate depending on the lighting conditions. This allows them to see and
hunt in bright or dim light.

Animals that aren’t hunters, such as goats,
cattle, deer, and sheep, have horizontal pupils, which give them better vision
to detect predators.