Kogia carries a sac off the lower intestine holding up to about twelve litres of dark syrupy fluid. Released through the anus when the animal is startled, it disperses into a persistent cloud in the water column. The whale then dives or sinks away behind it. No other cetacean is known to do anything comparable.
The rest of the animal is quietly odd as well. A pale crescent behind the eye, sometimes called a false gill, gives a passing resemblance to a small shark, and the underslung jaw and blunt head add to it. Kogia also produces narrow-band high-frequency echolocation clicks above the hearing range of killer whales, the same acoustic strategy porpoises use.
Direct observation is scarce. Pygmy sperm whales are among the most frequently stranded cetaceans in some regions yet are almost never seen at sea, so the ink defence is described from few encounters and from stranded animals.