A man's trip to the beach on Sunday left him scratching his head after stumbling upon a couple of shells with an interesting feature.
The Adelaide man visited Henley Beach, about 15 minutes from the city centre, when he discovered two shells with 'perfect circles' right through them.
"What's making these perfect circles in these shells?" he questioned, sharing a picture of them online.
The question prompted a flurry of responses from people also wondering the same thing, with many admitting they often see shells with holes too.
"I hope someone can answer this, my kids asked me the other day and I was like...," wrote one.
"Always wondered, never found out," said another.
Expert explains what creates the holes
Professor Culum Brown, from the School of Natural Sciences at Macquarie University, said as weird as it might look, these holes in shells are pretty common.
"There are actually loads of predatory snails out there, like moon snails, that use their radula — their chainsaw-like tongue — to drill through the shells of bivalves and suck out the gooey insides," he told Yahoo News Australia.
Bivalves refer to molluscs and include clams, oysters, cockles, mussels and scallops among others, and are a perfect meal for sea snails.
"You'll find heaps of these shells along the beach with these perfect drill holes in them," Professor Brown said.
"There is no way into a bivalve when it's closed, so these guys just go through it."
Sea snail behaviour: 'Disturbing and fricken cool'
The tongue of these carnivorous sea snails is specially designed for the purpose of drilling through the shells, according to the Dolphin Research Institute.
"It is a ribbon of tiny teeth that are rubbed back and forth across the shell," the website explains.
"The moon snail moves across the surface of the sand looking for the telltale siphons of a hidden bivalve. Once found, the bivalve retreats into its shell while the moon snail wraps its foot around the bivalve holding it tight, preventing escape."
After learning what caused the tiny holes, some people were amazed.
"This is both moderately disturbing and really fricken cool," one person wrote.
"Jeez, carnivorous snails — hopefully they stay in the water," said another.
Few joked the shells were from 'mermaid necklaces,' and it seems they're not far off as Professor Brown agreed the shells are 'handy' for making necklaces.
Do you have a story tip? Email: email@example.com.