She bounds along on all fours through long grass, panting with her tongue hanging out. When she reaches the tap she paws at the ground, drinks noisily with her jaws wide open and lets the water cascade over her head.

Up to this point, you think the young woman could be acting — but the moment she shakes her head and neck free of droplets, exactly like a dog when it emerges from a swim, you get a creepy sense that this is something beyond imitation. Then she barks.

The furious sound she makes is not like a human being pretending to be a dog. It is a proper, chilling, canine-like burst of aggression and it is coming from the mouth of a young woman dressed in T-shirt and shorts.

This is 23-year-old Oxana Malaya reverting to behaviour she learnt as a young child when she was brought up by a pack of dogs on a rundown farm near the village of Novaya Blagoveschenka in Ukraine. When she showed her boyfriend what she once was and what she could still do — the barking, the whining, the four-footed running — he took fright. It was a party trick that went too far and the relationship ended.

Miss Malaya is a feral child, one of only about 100 known in the world. The story goes that, when she was three, her indifferent, alcoholic parents left her outside one night and she crawled into a hovel where they kept dogs. No one came to look for her or even seemed to notice she was gone, so she stayed where there was warmth and food — raw meat and scraps — forgetting what it was to be human, losing what toddler's language she had and learning to survive as a member of the pack.

A shameful five years later, a neighbour reported a child living with animals. When she was found, at the age of eight in 1991, Oxana could hardly speak and ran around on all fours barking.

Though she must have seen humans at a distance, and seems occasionally to have entered the family house like a stray, they were no longer her species.

Judging from the complete lack of documentation about her physical and psychological state when found, the authorities were not keen to record her case — neglect on this scale was too shameful to acknowledge — even though it has been of huge and continuing interest to psychologists who believe feral children can help resolve the nature-nurture debate.

What is known about "the Dog Girl" has been passed down orally, through doctors and carers. "She was like a small animal. She walked on all fours. She ate like a dog," is about as scientific as it gets.

Last month, British child psychologist Lyn Fry, an expert on feral children, went to Ukraine with a Channel Four film crew to meet Miss Malaya, who now lives in a home for the mentally disabled. Five years after a Discovery Channel program about her, they wanted to see if she had integrated into society. Ms Fry wanted to find out how far the girl was still damaged — and to see a reunion with her father.

"I expected someone much less human," says Ms Fry, the first non-Ukrainian expert to meet Oxana. "I'd heard stories that she could fly off the handle, that she was very unco-operative, that she was socially inept, but she did everything I asked of her.

"Her language is odd. She speaks flatly as though it's an order. There is no cadence or rhythm or music to her speech, no inflection or tone. But she has a sense of humour. She likes to be the centre of attention, to make people laugh. Showing off is quite a surprising skill when you consider her background. In the film, Miss Malaya looks unco-ordinated and tomboyish. When she walks, you notice her strange stomping gait and swinging shoulders, the intermittent squint and misshapen teeth. Like a dog with a bone, her first instinct is to hide anything she is given. She is only 1.52 metres tall but when she fools about with her friends, pushing and shoving, there is a palpable air of menace and brute strength. The oddest thing is how little attention she pays to her pet mongrel. "Sometimes, she pushed it away," says Ms Fry. "She was much more orientated to people."

After a series of cognitive tests, Ms Fry concluded that Miss Malaya had the mental capacity of a six-year-old and a dangerously low boredom threshold. She can count but not add up. She cannot read or spell her name correctly. She has learning difficulties, but she is not autistic, as children brought up by animals are sometimes assumed to be.

Experts agree that unless a child learns to speak by the age of five, the brain misses its chance to acquire language, a defining characteristic of being human. Miss Malaya was able to learn to talk again because she had some childish speech before she was abandoned. At an orphanage school, they taught her to walk upright, to eat with her hands and, crucially, to talk.

Through an interpreter, Miss Malaya tells Ms Fry that her mother and father "completely forgot about me". They argued and shouted. Her mother would hit her and she would pee herself in terror. She says she still goes off by herself into the woods when she is upset. Although she knows it is socially unacceptable to bark, she certainly can.

Miss Malaya seems to be happy looking after cows at the Baraboy Clinic's insalubrious farm, outside Odessa. "It was dirty, terribly rundown and primitive," says Ms Fry, "but in Ukrainian terms, very desirable. Her carers are good people with the best interests of their charges at heart, though there is no therapy as such. Oxana is doing things she is good at."

It was here that the reunion with her father was staged a few weeks ago.

In the film, they stand awkwardly apart and it is ages before anyone speaks. Miss Malaya breaks the silence. "Hello," she says. "I have come," replies her father. The exchange is moving in its halting formality. "I thank you that you have come. I wanted you to see me milk the cows."