THE stink of flatulence and rotten eggs could provide a surprising lift for men. Hydrogen sulphide (H 2 S) causes erections in rats and may one day provide an alternative to Viagra for men.

The penis is packed with spongy tissue that produces an erection when it fills with blood. Nitric oxide (NO) helps relax the walls of arteries that supply the penis, allowing extra blood to flow in. Viagra works by blocking an enzyme that destroys NO.