 The "Wörterbuch der ägyptischen Sprache-(Dictionary of the Egyptian Language)" lists no less than 24 different terms of km indicating 'black' such as black stone, metal, wood, hair, eyes, and animals.The most common explanation for the hieroglyph is under the Gardiner's Sign List, section I for "amphibious animals, reptiles, etc" is a crocodile skin with spines.Rossini and Schumann-Antelme propose that the "crocodile skin" hieroglyph actually shows claws coming out of the hide.