Evidently there are a lot of stupid divers out there. From scubadiving.com:
Nurse Shark (Ginglymostoma cirratum)
During the day they are normally found sleeping on the bottom under ledges. They are one of the few sharks that have the ability to bite its tail. Because they look harmless, divers have been known to grab them by the tail, causing the nurse to turn and bite its tormentor. This has made the nurse shark the most common shark involved in human shark attacks. Fortunately it has very small teeth and the bites are seldom serious. On our shark dives the nurse sharks like to harmlessly cuddle up to divers. They range in size from 5' to 9', reaching a maximum length of 14'. They have two barbells on their upper lip. Both of their dorsal fins are approximately the same size and are set far back on their body. They lack a noticeable lobe on their tail. It feeds primarily at night on bottom-dwelling invertebrates, such as lobster and other crustaceans. Mating is in the spring. During this time, the female swims into shallow water to avoid mating with undesirable males. The males bite onto her pectoral fins and try to drag her into deeper water to mate. She finally submits when she decides the male is desirable. There are several areas in the Exumas where nurse sharks are known to mate.
