CAIRO // Some years back, Egyptian zoologist Samy Zalat was struck by a mystery in the boot of his car.
Each morning for about a week when he opened it to store his briefcase, he found a small pile of bones. Eeriness aside, he decided to open the boot in the middle of the night to see what he would find. A mouse? A rat?
"It was an Egyptian weasel," he said. "One of the great mysteries of Cairo."
The animal had gnawed a tiny hole in the boot after crawling through the metal underside from below. Each night it would bring its prey inside to eat in solace and leave the bones for others to clean up.
It is easy to miss the weasels in Cairo. These are among the quickest and smallest carnivores in the world and they usually come out only at night. But the rare experience of seeing one, usually at dawn or on a late-night walk, is usually enough to stop newcomers to the city in their tracks. One visitor exclaimed he had seen "an insane mongoose" on the street one morning. His expression was a mix of fascination and unease.
Weasels bound about, their long bodies zipping under cars and into crevices with the fluidity of a piece of string. They rarely interact with humans, except for a hissing sound they make when confronted or attacked. Their dens are often hidden deep in the basements of this metropolis of 17.5 million.
These avid hunters spend their nights searching for mice and rats, or devouring lizards and insects that cannot outrun them. Weasels are thin and long, making it easy for them to get where Cairo's street cats can only dream of reaching: rodent nests deep in burrows or cracks in the pavement. They have excellent hearing and sight, but a phenomenal sense of smell, scientists say.
Yasser El Boureidy, 30, a banker who lives in the Maadi neighbourhood of Cairo, said he had been fascinated by weasels since his childhood in Alexandria - where they also proliferate.
Egyptians have long known them for their ability to fit through openings "as small as a keyhole" and their terrible habit of urinating in the engines of old Fiats, which left a foul smell in the cars, he said. But there are other legends, too.
"Some people say they steal gold," Mr El Boureidy said. "If you drop a ring or an earring, the weasel will find it and hide it away."
By and large, Egyptians don't spend much time worrying about the creatures, who seem just fine with living side-by-side with city dwellers without interaction, he said.
But what is most striking is that they exist in Cairo at all and live side-by-side with humans - a phenomenon believed to be entirely unique to Egypt.
Carolyn King, an international authority on weasels and stoats at the University of Waikato in New Zealand, was shocked to hear that Egyptian weasels lived in the heart of Cairo.
"That makes Cairo one of the top towns on my bucket list!" she said, adding that their behaviour "confirms the suggestion that the Egyptian weasel really is a species quite different from any of the European and American weasels".
In 1992, zoologists discovered that the Egyptian weasel is its own species, the mustela subpalmata. It was found to be significantly different than the Saharan striped weasel, poecilictis libyca, a skunk-like animal that has been found in the deserts of North Africa.
The weasels' presence in Cairo has raised the question of how did they get here and when?
Richard Hoath, a lecturer at the American University in Cairo and author of a field guide to Egyptian mammals, said one possibility is that mustela subpalmata found its way to Egypt during a wetter time in earth's history. Like the short-tailed bandicoot rat - found to countries across Asia - which also exists in the western margins of the Nile Delta, the Egyptian weasel or an ancestor could have become trapped by the desertification of Sinai thousands of years ago.
The impact of the weasel on the ecology of Cairo is the subject of no scientific study, but Mr Hoath and Mr Zalat, the zoologist, believe it plays a crucial role in reducing the rat population in Egypt.
How else could a city with open rubbish heaps avoid the scourge of a rat infestation?
"I think it plays a major role in eradicating the rodents in the middle of Cairo, but how much?," Mr Zalat said. "We don't know. This would be a great doctorate dissertation."
In the world's largest cities, rats are the subject of great scorn and their extermination is a public policy priority because they carry diseases. The fleas that are drawn to rats are the real culprit, though. The bubonic plague that regularly ravaged much of the world until the invention of antibiotics in the last century was primarily spread by fleas that bit humans and infected them with the bacteria.
It's enough to propose a hypothesis: this little carnivore, the Egyptian weasel, protects Cairo like few others. It's a relief that it has never made it to the list of rodents for extermination.
Gay Talese, the writer of colourful stories about New York City, once examined the stray cats of his beloved city.
One anecdote is particularly revealing: "On the waterfront, however, the great demand for cats remains unchanged. Longshoremen occasionally tell stories of unhappy experiences with waterfront cats, and many hate cats - but they hate rats more. 'Once we had a guy here who couldn't stand cats, and he got rid of them,' said a workman on Pier 62, on Eleventh Avenue in the Twenties. 'Well within a day or so we started seeing rats all over the place. Every time you looked up you'd see a rat on a crate looking right down on you. They'd steal your lunch. Some of them seemed bigger than cats.'"
In some neighbourhoods of Cairo, such as the leafy Garden City area along the Nile that is home to many embassies, the Egyptian weasel proliferates more than in other areas.
But this reporter's attempts to chase one on a recent morning ended as quickly as the weasel appeared. Its brown fur, white on the bottom, flashed for a moment before bolting into the crevice on the side of a building smaller than a golf ball.
The mustela subpalmata, it seems, seeks no celebrity for its important work.