It might be irrational, but the lure of the doppelgänger is impossible to resist.

The idea of a shadowy double has inspired writers from Dostoevsky to Nabokov, and few can fail to be intrigued when a friend claims to have met their exact likeness on the bus.

For Sara Nordstrom and Shannon Lonergan, the two women pictured above, doppelgängers are neither fiction nor gossip, but reality. The two women are not related. They live more than 2,700 km (1,600 miles) apart—Sara is from Sweden and Shannon is from Ireland—and met through the website Twin Strangers, which is home to more than half a million people trying to find their lookalikes.

Members of Twin Strangers upload photos and catalogue their face, eye, and eyebrow shapes in a bid to find a match. And while Sara and Shannon are eerily similar—so much so that Shannon’s father “needed a moment” to tell the two apart, according to the Belfast Telegraph—they’re hardly the only people to find an unrelated lookalike.

Earlier this year, Niamh Geaney from Dublin, Ireland, met Karen Branigan, who lives just an hour away.

Niamh has since gone on to meet her second doppelgänger, and her third. Meanwhile, photographer François Brunelle has an entire series, “I’m not a look-alike” devoted to people who look like twins but are unrelated.

Statistically, any of these matches is a surprise. Researchers from University of Adelaide’s school of medicine collected data on eight facial measurements for 4,000 people and didn’t find one match. In their study, published in Forensic Science International earlier this year, they calculated that the chances of finding two people with eight of the exact same facial metric traits were less than one in a trillion.

But the study relied on measuring the exact distance between various facial features, rather than “descriptive” traits such as a curved nose.

“Descriptives are not considered a reliable method of evaluation because a trait such as the color of someone’s eyes is subjective,” said Professor Maciej Henneberg, co-author of the research, in a statement.

Which means, though it’s statistically almost impossible to find someone who is an exact match in terms of facial measurements, there’s a far higher likelihood of finding two people who look identical at first glance. So, while Sara and Shannon may not be exact physical replicas, they’re similar enough to be mistaken for twins.

Dr Daniele Podini, a forensic scientist and expert in facial recognition at George Washington University in Washington, told The Telegraph that what we see is strongly influenced by context. If two people have a similar physique, haircuts, and are dressed alike, we’re more likely to think they look alike thanks to “confirmation bias,” a psychological tendency to adjust facts so they fit the expected pattern.

Those hoping to find their own doubles can try appealing on social media, do a reverse Google image search and look through the “visually similar images,” or pay $3.95 per month to upload their photo and browse matches on Twin Strangers. Thanks to the wonder of the internet, we all have the chance to find our unrelated doppelgängers.