I think it is very funny that my cats growl when they have caught or stolen something that they want to keep for themselves. It is a surefire way to catch my attention and lose their 'prey-toy'. I have thought it several times when one of them has brought in a mouse or bird, but I am not letting them out at the moment because of bad weather and feral dogs, and tonight I heard that growl. I discovered that Persil had jumped on the counter and stolen a chicken breast that I had foolishly left there, though it was wrapped in cellophane. She of course ran out the room with it and I had to corner her in the bedroom to get it from her. If she hadn't growled I might never have known till it was too late. Needless to say, once I had recovered it, I cooked it and divided it carefully among all five cats!