I had a bite mark on my neck the day before a job interview. Also, my soon-to-be wife scratched my back once, and afterwards I put on a white shirt. About ten minutes later, she walked behind me down the hallway and noticed my shirt had bright red streaks from absorbing the blood from the scratches (Not for ten minutes, just the first few seconds). Of course, at the same time, I bit her on her shoulder and she developed a bruise that lasted for two and a half weeks.
They happen fairly often. Also seconding the body wash thing, though let me tell you that it's considerably worse when you work in a photo lab, have scratches on your arms on the something like two visible square inches of skin between your gloves and protective lab coat, and developing chemicals splash onto them.
