Bite mark on human skin from a Medicinal Leech showing typical Y-shaped pattern. These leeches have 3 jaws with roughly a hundred microscopic teeth. Leech saliva contains an anesthetic which makes the bite virtually painless, a vasodilator which expands the small blood vessels near the bite, an anti-clotting agent which can cause the wound to continue bleeding for many hours after the leech is removed, and even antibiotic agents to prevent infection.