I ran over a rabbit when I was a mere slip of a lad at 19... It upset me so much I had to stop the car until I calmed down.
The following day I was visiting my in-(out)laws who had just come back of holiday and bought me a present..... a little muumy rabbit and 2 baby rabbit ornaments!!! God, did I feel bad :(
The worst one I ever saw was a cat ran over by a garbage van - completely flattened this poor critter into the road, but missed it's tail, which was still swishing and twitching! Eeeeuuugh!