The black swallower might not be the best known undersea creature, but it might be one of the most abhorrent. That's because scientists have only ever seen them after they are dead—often after they have attempted to eat a fish so large that its meal eventually killed it through indigestion.
While scientists have never actually seen the fish eating, they speculate that it grabs its prey by the tail and slowly starts swallowing it whole, as its dinner rolls into a circle in its belly. Unfortunately, the black swallower is not too selective about the size of its prey, which often results in dinner starting to decompose before it can be digested. The resulting gas build up leaves the black swallower to float to the surface.