Why do animals move their ears when they hear a sound?

It is smaller animals that can move their ears in different directions. Such animals need to hear the sounds made by smaller predators. Larger animals do not need that skill and do not have it. Instead, humans depend more on sight. Humans frequently stay in herds with at least one looking behind for a predator. Other large animals stay in herds. They do not move their ears. Instead, they watch. The noise large predators make does not carry far. So, they do not hear a lion walking. They can see him coming.