In the 1970s Kemp’s discovery of otoacoustic emissions was not well-accepted; the notion of sounds coming out of the ear was incredible for most workers in the field who thought the ear was a passive linear mechanical sensor. Acceptance hinged upon the unconfirmed report by Rhode (1971) of nonlinear behaviour in the motion of the basilar membrane of squirrel monkeys. It was a very important result because it tended to explain the very fine tuning seen in the firing of primary auditory neurons. However, over a nine year period, numerous investigators tried to confirm it and failed, so that the notion that the outer hair cells were active, thereby producing the nonlinear behaviour, was very new and highly controversial at the time. The demonstration of similar non-linear behaviour in the cochleas of guinea pigs had a strong impact at a meeting in London in 1979, when LePage and Johnstone, 1980 confirmed the existence of nonlinear mechanical behaviour in a different species – guinea pig. The experimental result was absolutely hot-off-the-press, the week before the meeting and the paper was immediately accepted on a phone call from Brian Johnstone to David Kemp, and also to Peter Sellick in Sussex, who delivered the paper on our behalf. Members of the audience evidently responded spontaneously. This article in NATURE after the London Meeting records how the demonstration of nonlinear mechanical behaviour played a critical role in the discovery and acceptance of otoacoustic emissions.