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At 100 decibels, the love song of an adult American alligator is the loudest of all reptile calls. A deep-pitched roar means a big, powerful male. And for all other males in the vicinity, it is a call to arms they can't ignore. The males home in from far and wide to check the singer’s status and, if necessary, put him in his place. As more and more males muscle in to settle status issues, mayhem rules as there is a stretch of good breeding river at stake. Then the male chorus starts. It's alligator style Fame Academy where the winner gets the girls. But there's more to this concert than meets the ear. Below the water-line, the singing male shivers his flanks, producing a pulse of low-pitched frequencies that makes the water dance on his back. This infra-sound bass line isn’t designed to be heard but felt, like a pressure wave. It travels up and down the river, travelling further than the airborne bellow and affecting every alligator for up to a mile in both directions. Alligators’ lips are lined with tiny mole-like pressure receptors, sensitive to vibrations in the water. To a male, this infrasound signalling means competition. To a female, it probably feels like a seductive tingling in her lips. To her, the infra-sound solo is irresistable. Alligators may be ancient, but they are not primitive. Their sound system is the most complex in the reptile world. The female is inspired to make the first move and the solo turns to a duet.