Trichobatrachus robustus is the Wolverine of the amphibian world. You'll know when you've crossed the line because he'll gladly break his own bones to produce weapons to break yours. New Scientist reports on the findings of zoologist David Blackburn and his colleagues:
Trichobatrachus robustus actively breaks its own bones to produce claws that puncture their way out of the frog's toe pads, probably when it is threatened. [...]
At rest, the claws of T. robustus, found on the hind feet only, are nestled inside a mass of connective tissue. A chunk of collagen forms a bond between the claw's sharp point and a small piece of bone at the tip of the frog's toe.
The other end of the claw is connected to a muscle. Blackburn and his colleagues believe that when the animal is attacked, it contracts this muscle, which pulls the claw downwards. The sharp point then breaks away from the bony tip and cuts through the toe pad, emerging on the underside.