A 5ft bird that could, according to the RSPCA, kill a human with one strike of its 6in claws is on the loose in Kent.
South American rheas can kill with one strike of their claws
Ralph, a South American rhea, fled his enclosure in Benenden on Monday after his owner introduced pigs to his pen.
RSPCA spokesman Roy Jezard said the birds would also go for people's eyes with their beak, and said their strength was "unbelievable".
He added: "People want to pat them, but I don't recommend it. If you see it, report it to the RSPCA or the police."
Mr Jezard said rheas were not a problem in a paddock.
But he added: "Running up the street, with lorries, cars and dogs barking, they get startled and tend to kick out in defence, and can do quite a bit of damage."
Three rheas had originally escaped from their enclosure at the smallholding.
The owner of the flightless birds, Sue Savage, said: "I bought some pigs and introduced them to the rheas but the birds didn't like the look of them, leapt the 4ft fence and took off."
RSPCA officers captured one, which was 6ft tall, by manoeuvring it into a cul-de-sac using a van and dustbins. Another returned home of its own accord.
Mrs Savage said three-year-old Ralph was last seen on Hemsted Forest Golf Club, near Sissinghurst, on Monday.
"They can run up to 20mph and blend into the background quite well because they are dark grey.
"It would startle the hell out of you if you saw it."
She has put up wanted posters around Benenden and warned local farmers to be on the lookout.
The birds were naturally tame and could be kept without a licence, she added.
"Generally they're placid but it's when they get spooked that they can become a different bird and I wouldn't want to grapple with one unless I was a professional."
She said the birds were kept for their eggs.
"They lay between 200 and 300 each year and these sell on Ebay for £30 each."
Mrs Savage, 44, and her husband Mike, 46, keep 10 rheas at their farm as well as pigs, chickens, horses, sheep and geese.