Tom Borum was trying to beat the heat with a cool dip in the Atlantic when - Zaappp! - a nasty little sting hit him right in the calf.
Borum heard his fiancee cry out. Something zinged her beneath the waves as well, leaving a trail of red marks behind.
They scrambled back to the beach Thursday and found others smarting from similar attacks. One little girl screamed on the sand as her mother tried to comfort her.
"I've been coming here since I was born," said Borum, a 59-year-old visitor from Maryland. "I've never run into this kind of thing."
Welcome to the invasion of the jellyfish.
Hundreds of stings from these translucent blobs have been reported along the Charleston County coastline since last weekend. Some suspect a swarm of jellies rode in with strong onshore winds and roiling surf. Others wonder if a shift in the Gulf Stream or this week's blast of thunderstorms are to blame. Whatever the reason, they hit the coast - in force.
"We've had a dramatic increase in stings this week," said Nikki Bowie, safety program manager for the county Parks and Recreation Commission. "It's not only the number of stings, but the severity."
The same had not been reported along some Grand Strand beaches as of Friday, even as jellyfish advisory signs were posted on the beach at Myrtle Beach State Park, according to Janna McCrary, summer naturalist at the park. She couldn't be sure what prompted the advisory.
Nicole Aiello, spokeswoman for the city of North Myrtle Beach, said there also has not been an unusual increase in jellyfish sightings there. She couldn't say whether reports of jellyfish stings were increased.
The beach parks in the Charleston area normally see just a couple of reported stings a month, if any at all.
Isle of Palms, however, had 162 reported stings last Sunday and another 186 jellyfish run-ins on Tuesday. The number of reported stings on Folly Beach jumped from 15 on Wednesday to 150 the following day, Bowie said. Several stings also were reported at Beachwalker Park on Kiawah Island, she said.
Among the reports is at least one unconfirmed run-in with a dreaded man o'war, the unofficial king of sting.
Trevor Wagner, 21, got stung four times in 30 minutes while surfing Friday at Folly Beach. He wouldn't recommend the experience.
"They don't hurt for very long, but they definitely hurt in those initial minutes," he said.
Lifeguards are stocking up on vinegar to take the zing out of stings and are flying purple flags to warn swimmers of the threat, Bowie said. Folly Beach officials also planned to place a jellyfish warning sign at the entrance to town.
No one is sure how long this will last. It likely depends on the wind and currents. "Hopefully, they will be gone soon," Bowie said. "This is the longest stretch I can remember."