This neighbor from Amen Farm down the road got us thinking about eyes — actually, the differences in some eyes.
Big cats (e.g., cheetahs and lions) and big canines (e.g., wolves and dogs) have round pupils, as do humans.
Cheetah Zoo Captive
Siberian Husky
House cats and other smaller predators (e.g., foxes) have pupils that can become vertical slits.
Goats and some other grazing animals have horizontal rectangular pupils.
The latest theory apparently is that rectangular pupils give grazers, such as goats, a wider side-to-side view to see approaching predators. Pupils that can become vertical slits maximize the leaping and striking of wait-and-pounce ambushers that have eyes relatively close to the ground, such as small cats and poisonous snakes. Round pupils maximize the accuracy of larger predators that historically have needed a “full-frame” view to find and run their prey down, such as big felines, canines, and early humans.
Of course, nowadays, the prey that many domestic dogs run down may be something like a tennis ball and domestic cats never show their snake eyes when posing comfortably:
(Brooklin, Maine)