to protect themselves against swarms of sexually aroused male frogs, the female frogs stiffly extend their arms and legs away from the body, keeping incredibly still until the male releases them from its grasp.

Mating frogs may have been occasionally getting it wrong for hundreds of millions of years. We know that males today will sometimes select an inappropriate partner during the breeding season – a frog from a different species, a turtle, a fish or even an inanimate object. Now there is evidence that these mistaken attachments could be an ancient feature of frog reproduction, arising early in the amphibians’ evolution.

Frog mating is often hard to miss. In most species it involves a process called amplexus, in which males grip onto a female tightly for hours or days at a time until the eggs are fertilised. But there are plenty of records of male frogs grappling an unpromising target such as a frog from a different species or a dead individual. One explanation is that such mistakes are more likely to happen in species that breed in large numbers with a low ratio of females to males, and where multiple species occupy the same breeding pond.

Konrad Lorenz once observed a Shell Parakeet who grew amorous with a small celluloid ball. And many other animals exhibit mating behavior toward what researchers refer to as "biologically inappropriate objects." Bulls will treat almost any restrained animal as a receptive cow. Their general rule in life seems to be, "if it doesn't move away and can be mounted, mount it!"

During the early 1950s, researchers at Walter Reed Army Medical Center surgically damaged the amygdala (a region of the brain) in a number of male cats. These cats became "hypersexual," attempting to mate with a dog, a female rhesus monkey, and an old hen. Four of these hypersexual cats, placed together, promptly mounted one another.