The Hairy Frog
Also called the horror frog and the Wolverine frog, the hairy frog sprouts claws on its hind feet. These aren't "true" claws because they lack a keratin coating, and are made entirely of bone. They emerge through the toe pads when the frog contracts a specific muscle, forcing the claws downwards and breaking the collagen bond between them and the toe bones.
Key Facts In This Video
The hairy frog breaks its own bones to force keratin claws through its skin. (0:21)
The bones break when the frog feels threatened and contracts a muscle that moves the claws downward. (0:35)
Scientists theorize that the frog retracts the claws back into its body when its muscles relax. (0:50)