At the aquarium, we watched two dolphins torture a fish. They'd held it with their teeth in a way that tore the scales off, and let it bleed. But they didn't bite it hard enough to kill it or to even take a bite for food. One sees footage of dolphins killing porpoises for fun or of a gang of young male dolphins holding a female down for rape, but to see this sort of thing for yourself brings it home a bit. Sharks would never do this. Note the bits of tissue, blood, and scale floating around the half-dead fish. Wonderful.