"Terrible claw" refers to the unusually large, sickle-shaped talon on the second toe of each hindfoot. The fossil YPM 5205 preserves a large, strongly curved ungual. In life, archosaurs have a horny sheath over this bone, which extends the length. Ostrom looked at crocodile and bird claws and reconstructed the claw for YPM 5205 as over 120 millimeters (4.7 in) long. The species name "antirrhopus" means "counterbalance", which refers to Ostrom's idea about the function of the tail. As in other dromaeosaurids, the tail vertebrae have a series of ossified tendons and super-elongated bone processes. These features seemed to make the tail into a stiff counterbalance. Still, a fossil of the very closely related "Velociraptor mongoliensis" ("IGM" 100/986) has an articulated tail skeleton that is curved laterally in a long S-shape. This suggests that, in life, the tail could bend to the sides with a high degree of flexibility. In both the Cloverly and Antlers formations, "Deinonychus" remains have been found closely associated with those of the ornithopod "Tenontosaurus". Teeth discovered associated with "Tenontosaurus" specimens imply they were hunted, or at least scavenged upon, by "Deinonychus".