Asparagus, oysters, chocolate and bird's nest soup are all well-known aphrodisiacs, but the Penguin Atlas of Human Sexual Behaviour lists some other, rather surprising foods that are supposed to increase sexual desire. The liver of the deadly fugu, or puffer fish, is famously eaten by the Japanese to increase virility. Unfortunately, it's sometimes the cause of their death. The cantharis beetle is ground into a fine powder known as Spanish fly, which stimulates the bladder and urethra. The tingling that follows is supposed to be sexually exciting, but can be dangerous. The Marquis de Sade laced sweets with Spanish fly, which led to the phrase: 'Never take sweets from a stranger.' Swan meat has been favoured as an aphrodisiac because of the birds lifelong fidelity. Others prefer rabbit meat, because rabbits are famed for their sexual profligacy. Hippopotamus meat is a favourite in Africa. Rocket was sown around the base of statues of Priapus - the Greek god of fertility - to restore vigour to the genitalia. In medieval times, the Church banned its cultivation in monastic gardens. Early sex manuals included recipes for preparing the genitalia of dogs, bulls, deer and alligator. Goats' testicles, boiled in milk, are popular in India.