A family were "freaked out" after rewatching a holiday video to discover a "sea monster" popping its head out of the sand and "waving" to their young son.
Debbie Clintworth decided to record parts of their recent trip at the Haven Greenacres Holiday Park near Porthmadog, Wales.
But when they got home to watch back their adventures, they couldn't believe what they saw.
It wasn't until reviewing the footage she had taken on the beach that Debbie noticed the strange creature in the sand, North Wales Live reports.
In the background of a video of her five-year-old son Joseph running across the nearby Black Rock Sands beach and splashing in a stream, a mysterious creature seems to pop out and wave its head as if to say hello.
Debbie, from Liverpool, who was also on holiday with her husband Stephen and his father, said she did not notice the 'creature' when she was filming.
But after uploading the clip to Instagram, neither she nor her friends can make out what it is, leading them to dub it the "Morfa Monster".
“I never even noticed it on the day,” she said. “I posted the clip on my Instagram account and it was only when watching it back later that I saw it. I was like, 'oh my God, what is that!?' It freaked me out a bit.
“From the video, it looks like the thing turned its head when my little boy made a splash in the stream. I reposted it and some friends messaged me saying they’d also seen it but hadn’t liked to say anything!”
The video was taken at low tide, with the water's edge some distance away from where the family were walking. Debbie admitted she had been "baffled" by the clip, with locals also flummoxed about what the creature could be.
“There weren’t many people on the beach as it wasn’t that warm," she said.
"There were just a few people walking by the sea. Some people have suggested it might have been litter blowing in the wind. But the weather was calm and there wasn’t much wind at all. It’s really baffled me.
"I mean, there are always lots of wormholes in the sand but it was nothing like that. I wanted to find out what it was, which is why I shared the clip on the Abersoch Facebook page in case any fishermen or boat owners had any ideas.”
But after sharing the video on Facebook, Debbie is no closer to discovering the truth, although plenty of local residents have been left scratching their heads in unison.
While jellyfish, crabs and moles were all put forward as possible suspects, other people were left shocked, with one saying: "I‘ve never seen anything like that, moves a bit like a fish head.”
Given the unenviable task of providing some kind of explanation was Frankie Hobro, owner and director of Anglesey Sea Zoo.
She has plenty of experience of dealing with marine oddities, having established a research programme to explore different coloured lobsters being found around the UK coast.
While she said it was "impossible" to provide a definitive answer from the grainy footage, she had one or two theories about what the creature could be.
“One possibility is that it shows a seabird looking away," she said. "But that’s unlikely given its size.
“Another is that it is a lugworm cast, which tend to appear at low tide near rockpools or streams where the sand is wetter. The casts tend to be conical in shape and are darker in colour because of the wet sand.
"Within the cast, a crab might be half buried and its movements might cause the cast to shift.
"Alternatively, there might be litter on the cast which is disturbed by changes in air pressure below the sand, caused perhaps by a lugworm, crab or even the boy running past.
"It’s hard to know exactly what it might be without more evidence – it’s a bit of a puzzle. But there will be a rational and mundane explanation. Whatever it is, it’s good to see people taking an interest in coastal marine life."
