Consist mainly of undigested clotted blood. As the dog or cat moves around, flea faeces fall from the coat and provide food for flea larvae in the environment. Flea faeces in the coat are usually the main sign of a flea infestation. If the coat is brushed onto some damp kitchen paper, flea faeces will be seen as small brown/black particles that leak small amounts of dark red blood on contact with moisture.