The woman volunteer thought Nim was coming to hug her, but instead the young chimp lunged, biting so deep into her cheek that his fangs pierced her mouth. As she clutched her bleeding face, the little ape was beside himself, using the same piece of sign language again and again to attract her attention. 'I'm sorry, I'm sorry,' he repeated.
This haunting recollection is one of many contained in a riveting new film, Project Nim, by the director of the Oscar-winning Man On Wire, about one of the most bizarre scientific experiments of recent times.
Monkey business: Nim is taught sign language by volunteer Joyce Butler
British film-maker James Marsh's latest subject undertakes a journey every bit as astonishing as tightrope artist Philippe Petit's walk on a wire strung between the Twin Towers of New York's World Trade Centre.
Nim was a chimp that was raised as a human child in order to test out the radical theory that man and his closest relative could learn to talk to each other.
Tragically, as Marsh's film relates through a mixture of archive footage, re-enactments and interviews with those who took part in the early-Seventies experiment, this is a tale that ultimately says more about human arrogance than simian intelligence.
For those who have been charmed by the recent tale of Digit, the gentle adult gorilla that shares the marital bed of the devoted French couple who look after him, here is a much darker side to mans attempts to bond with his ape cousins.
A helpless pawn ripped quite literally from his mothers breast, Nim was a victim of the naïve, hippy- culture-infused world of early-Seventies New York.
He fell into the clutches of a hapless band of woolly social scientists who gave him human clothes, human food and enough doting young lady volunteers to send his simian hormones haywire. If it were not for what happened later, it could have been a Woody Allen comedy.
'A heartless Doctor Doolittle': Professor Herb Terrace takes Nim for a ride
Project Nim began in November 1973 with Nims birth at a primate research centre in Oklahoma. He spent just a few days in the arms of his real mother before she was knocked out with a tranquilliser dart and her screaming baby was handed straight to his delighted new, human, mother.
Nim had been selected by Herb Terrace, an ambitious psychology expert at New Yorks Columbia University, to prove a premise that was way out even for the Seventies: that a chimp raised as a human and taught sign language could learn to communicate in grammatical sentences. Finally, man might understand what animals were thinking and perhaps vice versa.
Terrace, a small, mustachioed man with a huge ego, had named the little creature Nim Chimpsky a pun on Noam Chomsky, the famous thinker who insisted that only humans have the capacity for language
However, Terrace thought differently and had chosen Stephanie LaFarge, a former student and lover, to bring up Nim in the large Manhattan townhouse she shared with her self-confessed rich hippy writer husband, Wer, and their seven children.
But it was a disastrous decision Stephanie never bothered trying to discipline Nim. She did not take any notes on the experiment and did not keep a log of Nims progress, but she did breastfeed him and give him alcohol and puffs on her cannabis joints.
He was encouraged to lay waste to their expensive home and wind up his rival for her affections, Stephanies husband. Home movie footage shows the little creature, a blur of black and white in his romper suit, charging around as Stephanie recounts dreamily how she let him explore her naked body as he moved into puberty.
I never felt sexually engaged with him, she recalls, which is a blessing at least. Yes, it certainly was the Seventies.
The snapshots of those halcyon early days would grace any family album baby having a nap, playing with the cat, trying out the lavatory (with sporadic success) or simply staring adoringly into the smitten eyes of the women who queued up to cuddle him.