I ran over a cat once in my truck. I knew I had hit something, so I pulled over at the next parking lot and started looking around. Got to the passenger rear quarter panel and saw blood on my tire, so I knew I hit something but I couldn't find any evidence of a body when I scanned the road. So I went inside a store (which is where I was heading in the first place) and came back out. That's when I noticed "parts" were dropping out of the wheel well. Needless to say, the cat (or most of him) was still stuck in the top of the wheel well and I had to scrape the remains free after I got home.
My dad told me the only thing that happens to a dead cat is it just gets flatter, but I had to disagree with him on this one.