When Thomas Douglas took his seat on a flight from London to Galway last year he did a double take. The stranger seated next to him was his spitting image, bushy red beard and all.
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But what are the odds of having a doppelganger?
According to Adelaide University forensic anthropologist Teghan Lucas, the chance of two people looking the same is not as common as an internet search suggests: it's a rather slender one in a trillion.
Dr Lucas' research also looked at which was more unique: a person's face or their body. Using the US Army's Anthropometric Survey database of almost 4000 soldiers, she found people were more likely to have a "stranger twin" who shared their facial features than their body shape.
The chance of people sharing the same eight body measurements, such as calf circumference, forearm length or hip breadth, was one in a quintillion (a one followed by 18 zeros), she said.
"What this research is saying is, 'Start looking at the body. It's very useful,' " Dr Lucas said. "It's the first paper of its kind to say that."
She said anthropometry, or measuring the human body, had practical applications for police and other law enforcement agencies that want to match crimes with perpetrators or locate missing people.
Dr Lucas, who has appeared as an expert witness in court trials, said body measurements were scientifically as unique and valuable to investigations as DNA or fingerprints.
However, because humans have evolved to recognise faces, there existed an over-reliance on facial features to identify people in criminal and missing person investigations.
Dr Lucas said her research proved body shape could be more useful than facial recognition because the body was more likely to be unique.
"People are leaving their anthropometry at a crime scene when they are caught on CCTV camera or take an incriminating selfie," she said.
"Studying human variation is not new but what is new is that we can now get body measurements from camera footage and we can use those measurements to identify individuals."
She said there needed to be more collaboration between law enforcement or defence authorities and academics to develop computer models and programs in what was an emerging field of science.
"Applying knowledge of human variation to images rather than skeletal remains is a relatively new area," she said.
The US Army's Anthropometric Survey, known as ANSUR, is a database going back more than two decades. It was created to keep track of eight body and eight facial measurements of soldiers but has become a useful resource for researchers.
