Because such a reaction in nature provides (a) safety and (b) food.
In addition, the cat's hearing is much more powerful than that of a human. The frequency range is three times wider (up to 60,000 Hz), and no one has defined the threshold sensitivity. For comparison, a dog's hearing is rougher than a cat's, but its sensitivity is 16 times higher than that of a human. So those sounds that you and I think of as rustling sound like a tocsin for a cat.
Because such a reaction in nature provides (a) safety and (b) food.
In addition, the cat's hearing is much more powerful than that of a human. The frequency range is three times wider (up to 60,000 Hz), and no one has defined the threshold sensitivity. For comparison, a dog's hearing is rougher than a cat's, but its sensitivity is 16 times higher than that of a human. So those sounds that you and I think of as rustling sound like a tocsin for a cat.