A few years ago I kitty sat for a friend. Her cat was a very small black male and I had Fred and Webb, both usually very kitten friendly. He had a bell, and they kept smacking him around, but no hissing or signs of aggression. After a little while of this, I removed the bell and they stopped smacking the poor little thing. The only thing I could figure is maybe they thought he was a toy or just hated the bell. They were fine with him as soon as the bell was gone.