Background via Collision Detection:
Okay, so -- the Seattle aquarium had a couple of Giant Pacific Octopi, and for logistical reasons they had to temporarily put one of them in a tank holding several sharks. They figured the octopus would be okay because it can change color to conceal itself from predators. But over the next week, the marine scientists came into work to find sharks are lying dead on the floor of the aquarium. Whatever was going on? They stayed around one evening and trained a camera on the water to see.