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Blood

A few species, specifically the common, white-winged, and hairy-legged vampire bats, feed only on animal blood (hematophagy). The common vampire bat typically feeds on large mammals such as cattle; the hairy-legged and white-winged vampires feed on birds. Vampire bats target sleeping prey and can detect deep breathing. Heat sensors in the nose help them to detect blood vessels near the surface of the skin. They pierce the animal's skin with their teeth, biting away a small flap, and lap up the blood with their tongues, which have lateral grooves adapted to this purpose. The blood is kept from clotting by an anticoagulant in the saliva.