Evil implies sin and a conscious choice to commit sin, knowing the difference between good and evil.
Animals cannot sin.
They suffer the effects of a fallen world but they do not and can not sin, nor can they be “evil”.
Evil is a choice reserved solely for humans.
[although a cat joyously, slowly and meticulously dismembering some small animal could be said to offer a fair imitation of ‘evil’]
Semantics.
When I saw that cat behave the way she did, there is no better word than “evil”. Luckily she wasn’t constantly attacking, though.
As far as the silly mouse-playing thing, now you are projecting your morality on the natural behavior of an animal, and I doubt cats are the only ones. Not that I really care, either. None involved is human.