Despite being the sexiest member of the X-Men (with the possible exception of Cable), Wolverine is also the most vicious. He doesn't have x-ray vision or psionic powers, he is just the perfect superhero: rapidly healing, strong and immensely tough. In fact, the only thing mutant about him is his ability to rapidly heal - which enabled adamantium to be grafted to his bones, as seen in Figure A:
Notice the extendable and retractable claws, that though they appear to have claw condoms built into his costume, still apparently (according to the movie and some additional material) hurt like hell when he extends them.
This quality only appears to be found in one other species - the Arthroleptidae - a type of toad found in remote parts of Africa. Apparently, they have claws. Also apparently, unlike cats, there is no sheath covering the skin to ease the extension of the claw, but only a small bone that disables it from coming out accidentally. So when the poor frog gets threatened, it not only breaks a bone, but a claw comes shooting out of its skin. This is the only vertebrate thats claws need to pierce skin to come into use. Observe in Figure B:
Perhaps both the frog and Wolverine use their claws to physically manifest the emotional pain of being a mutant. And I wonder if you can hear the claws both go *SNIKT*. See the two below in Figure C: