Excessive violence done right!
I've always enjoyed this song. A cheerful, upbeat melody and cute, simplistic lyrics contrasted with some pretty dark subject matter. By presenting us with cute characters, bouncy motion, and quick glimpses of extreme gore, this animation achieves the same dichotomy as the Beatles' hit.
What else is there to say? The timing is superb. The look of the movie is great. And, oh yeah, I laughed my ass off.