Oysters have been considered an aphrodisiac for years. The Romans documented oysters as an aphrodisiacal food in the second century A.D as mentioned in a satire by Juvenal. Aphrodisiacs were first sought out as a remedy for various sexual anxieties. Procreation was an important moral and religious issue and aphrodisiacs were sought to ensure both male and female potency. Despite long-standing literary and popular interest in internal aphrodisiacs, there is nothing in the oyster that causes sexual arousal. In reality, oysters are very nutritious and high in protein. One hypothesis is that the oyster resembles the female genitalia. The psychological impact of believing that oysters are aphrodisiacs is sometimes strong enough to produce, at least temporarily, greater sexual desire or performance. Raw bull's testicles ("prairie oysters", as they are called), clams, celery, or tomatoes are also considered aphrodisiacs.