I slit my fingertip, hard. And I slit it on a sharp metal, and it actually cracked the nail, penetrating it and stabbing the skin under the nail, which bled like hell. It hurt pretty bad. I had to put Coffee Powder on it to stop the bleeding and numb the pain. It healed in two weeks.
EDIT: After I put coffee powder on my fingernail, I saw dry blood on the doorknob that was my blood when I touched it.