They appear on the sand like any old piece of sea detritus. Sometimes they're found, amid the candy wrappers and cracked shells, by volunteers cleaning up the area. Other times a vacationer might glimpse the grisly discard from the corner of their eye, a serene walk along the beach interrupted just like that.

As more people learned about these discoveries, they attracted morbid scavengers to the Pacific Northwest shorelines, where the Salish Sea connects waterways along the West Coasts of the U.S. and Canada.

What these scavengers sought remains a prickling curiosity: severed feet attached to running shoes, washed up from origins unknown.

Sixteen of these detached human feet have been found since 2007 in British Columbia, Canada, and Washington state. Most of these have been right feet. All of them have worn running shoes or hiking boots. Among them: three New Balances, two Nikes and an Ozark Trail.

The most recent one turned up earlier this week.

Charlotte Stevens of British Columbia was taking a walk with her family on Vancouver Island, the CBC reported, when her husband spotted something in the sand.

It was shoe, that they could see right away. But a closer inspection revealed something more.

"He picked it up and brought it out on to the beach," she told CBC, "and we had a look at it for about five minutes and we thought, it almost looks like there is an actual foot bone in it."

Sure enough, the B.C. Coroners Service confirmed that the shoe came with a dismembered foot. As with the others, there's no telling for exactly how long the foot was in the water, but the regional coroner Matt Brown said the exact model of shoe had gone on the market after March 2013, indicating that it once belonged to someone who went missing between then and last December.

Brown is working with the police to connect the foot to individuals who disappeared from the area around that time.

If history is any indication, however, the identity associated with the foot will stay adrift.

Over the years, armchair sleuths and scientists alike have used a number of terms to describe the feet: severed, dismembered, detached, disarticulated.

Found, but still lost.

After the first two feet — both right — were found in British Columbia just six days apart from one another, locals began sounding the alarm, and authorities expressed equal surprise.

"Two being found in such a short period of time is quite suspicious," Corporal Garry Cox of the Oceanside Royal Canadian Mounted Police told the Vancouver Sun in August 2007.

"Finding one foot is like a million to one odds," Cox said, "but to find two is crazy. I've heard of dancers with two left feet, but come on."

Five more were found in the next year, including one near Pysht, Wash. Speculation increased, as recounted in a 2008 article in the Toronto Star:

"Speculation ranges from natural disasters, such as the tsunami of 2004, to the work of drug dealers, serial killers and human traffickers.

Loading... Loading... Loading... Loading... Loading... Loading...

"One theory concerns a plane crash off Quadra Island three years ago with five men aboard. Only one of the bodies has been found.

"Other theorists believe the coastline is being used as a body dump for organized crime activity; a third scenario is a serial killer is at work."

But to the disappointment of many a conspiracy theorist, science suggests more mundane answers.

Writing for the Pacific Standard, Spenser Davis pointed out last year that a study on the Puget Sound found that when a body floating in water is "subjected to the push and pull of its environment," the bones of hands and feet are almost always the first to fall off.

In British Columbia, two of the feet have since been identified as having belonged to people with mental illness, while three others were linked to individuals who likely died of natural causes.

Foul play is not suspected in any of the other cases, though it hasn't been ruled out, either.

"All of the ones who've been identified so far, there's no mystery," Gail Anderson, a criminologist at British Columbia's Simon Fraser University, told the Daily Beast in 2011. "These people were very depressed, unhappy about life, and were last seen heading toward the water. People jump off bridges. They deliberately wish to disappear."

But there are other points of strangeness. For one, why did the feet only start turning up after 2007, and why have they continued to turn up with unprecedented frequency since then?

The Daily Beast considered the power of the "Vicious Cycle" theory, which suggests that once people became aware of the phenomenon, they started subconsciously — or completely deliberately, in some cases — scanning the shorelines for shoes.

Also a likely answer.

And yet — it's hard not to wonder.

"There are so many coincidences taking place," forensics consultant Mark Mendelson told the Daily Beast in 2011. "Everybody who jumps off a bridge is wearing runners? ... Until you can show me something pathologically concrete that this is a natural separation of that foot from a body, then I'm saying you've got to think dirty."