I just noticed after I cut my nails there that my thumbnail has detached from the nail bed near the tip of my right thumb. I think it's from years of using it as a tool to peel citrus fruit; often the rinds are quite hard or the space beneath the nail gets filled with pith which acts as a wedge, and the strain on the nail and nail bed enough to cause a very slight separation and a little bleeding, which must not fully heal, leading to further separation the next time it happens.