It is a joke, not real, some people happen to find things funny that would never happen. If you've had a cat scratch your new Corvette (as my dad did) you might find some humor in a car that could take revenge. I am not saying I would wish the cat decapitated in real life, but this is TV folks, we can do things on TV we wouldn't do in real life or want done. I know many people who have wanted to off a obnoxious cat or two, but never would, this feeds that fantasy in a non-violent manner.
I don't think it matters that it is a cat, dog, squirrel, or whatever animal, it is a very clever idea. The gal I sent it was totally shocked in horror when she saw it, then about 5 minutes later she was laughing her butt off. If you are of the "sensitive" type maybe I can see being offended, maybe I am just a insensitive @ss, or maybe becuase it is because I was raised on a farm and I've seen much worse happen in real life, but I think it was funny as anything I've seen in a long time.