The head of fish was found in Fiji and it seems that this fish decided to have for breakfast fish-urchins, but something goes wrong. When fish-urchin is attacked she fuel her body with water and became dangerous for her enemies. When big carnivorous fishes try to swallow such a ball, they ends tragically.

Cymothoa exigua is a parasitic crustacean of the family Cymothoidae. It tends to be 3 to 4 cm long. This parasite attaches itself at the base of the spotted rose snapper’s tongue, entering the fish’s mouth through its gills. It then proceeds to extract blood through the claws on its front three pairs of legs. As the parasite grows, less and less blood reaches the tongue, and eventually the organ atrophies from lack of blood. The parasite then replaces the fish’s tongue by attaching its own body to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue, except that it has to share its food with the parasite. It appears that the parasite does not cause any other damage to the host fish. Once Cymothoa exigua replaces the tongue, it supplements its diet with food particles, thereby relieving strain on the host’s circulatory system. This is the only known case of a parasite functionally replacing a host organ.

Text from WikipediA