Cats predate Egypt, but were venerated in Egyptian cultures. No animals are a sign of hell unless made that way by humans. Cats, like us, are created by God.
No. The cats were a revered animal and even a domestic pet. They were associated with certain dieties but were certainly not considered evil or connected to hell (the Egyptian concept of which was not the same as out current one anyway). Mummy cats were revered, hence their being preserved.
