What do you think is the worst offense a film can make?

Im a dog lover and I always hate to see dogs get killed on film. I know its fake but I still dont like seeing it. There is a film called Stitches that I was really liking until a scene where the main villain beats a cat to death. I lowered my would be rating after that.

I know Cannibal Holocaust (which I do very much like) had actual animal deaths but luckily there is a version on the DVD that excludes those scenes.