When surfer Jeff Weakley noticed a blister-like bulge in his foot last summer, he put it down to too much running.
He didn't think much more of it - but as it began to grow, he began to pick at it.
Eventually, he managed to tweeze it open and found a small fragment of shark tooth, left behind after a close encounter with the scariest predator in the sea almost 25 years earlier.
And another surprise was to come. After sending the 2.5mm tooth fragment off for analysis, DNA testing was able to identify the type of shark that had bitten him as he surfed off Florida's Flagler Beach in 1994.
"I was very excited to determine the identity of the shark because I'd always been curious," Weakley, editor of Florida Sportsman magazine, tells the Florida Museum of Natural History.
"I was also a little bit hesitant to send the tooth in because for a minute I thought they would come back and tell me I'd been bitten by a mackerel or a houndfish - something really humiliating."
But Weakley's bite was the real deal, caused by Carcharhinus limbatus - a blacktip - a shark species commonly involved in bites in Florida.
Weakley was planning to turn the sliver of tooth into a pendant but when he read about how researchers in the Florida Program for Shark Research identified the shark species responsible for a bite off New York by analysing DNA from a tooth retrieved from the victim's leg.
Gavin Naylor, director of the program, said it was a surprise there was any DNA left on the tooth after it had spent such a long time in Weakley's foot.
"I had put our odds of success at slim to none," he said.
Laboratory manager Lei Yang who said he thought "it was kind of weird" to test the tooth, but added: "It was a mystery waiting for us to uncover."
Yang cleaned the tooth of contaminants, removed part of the enamel and scraped pulp tissue from the tooth's cavity.
He extracted DNA from the tissue and made a genomic "library" out of it.
He compared the target sequences against two databases of shark and ray genetic information to determine Weakley had been bitten by a blacktip.
About 70 per cent of shark bites are caused by unidentified species.
As for Weakley, he said he was back in the water - foot encased in a waterproof bandage and bootie - within a couple of weeks of the original incident.
Twenty-five years later, he surfs and fishes weekly and regards the sharks he frequently sees in the same light as dogs that menace him when he jogs.
"I certainly don't have a hatred of sharks or any feeling of vindictiveness toward them. They're part of our natural world," he said.