Presence of fine, white, leathery froth seen at the mouth and nostrils is one of the most characteristic external signs of drowning. It is white or rarely blood stained, lather-like, abundant and increase in amount with compression of chest. Even after wiping it gradually reappears, especially if pressure is applied to the chest. Froth is also seen in strangulation, acute pulmonary edema, electric shock, during epileptic fit, in opium poisoning and putrefaction. But in all these cases the quantity of froth is not as large as in drowning, and the bubbles are also much smaller. Ref: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 6th Edition, Pages 3.66-3.67 ; Essentials of Forensic Medicine and Toxicology By Dr K S Narayan Reddy, 27th Edition, Pages 325-6