Reminds me of a weird story...
One time I was playing sonic 2 on my Genesis. I had been playing for hours, and I had finally beaten Robotnik on Mystic Ruins. I jumped on the animal capsule thingy, but instead of animals, a bunch of bloody gibs started jumping out of it. It scared me so much that I turned off the system and left.
Now that I think about it, it was probably just some scrambled sprites, like when the cartridge contacts are dirty. It was scary at the time though.....