Why I am a 'killer clown'
You're on your way home. It's dark. Out of the corner of your eye you see a figure lurking menacingly. As your eyes adjust to the gloom, the figure eases into focus - it's a clown.
Clown sightings have become an increasingly common occurrence in the US, Australia and Canada. And, fuelled by social media, they are now on the rise in the UK too.
Thames Valley Police responded to 14 separate clown-related incidents on Sunday, while in Norwich, a man was arrested after an incident in which someone dressed as a clown terrified a woman in a park.
In Durham, four children were followed to school by a clown armed with a knife.
But what motivates someone to put on a clown mask and terrify strangers?
Matteo Moroni, 29, from Perugia, Italy, is the owner and director of YouTube channel DM Pranks. He's been terrifying unsuspecting passers-by for three years in a series of frightening videos that have racked up hundreds of millions of views on the video-sharing website.
His videos are typically shot at night in remote, eerie locations - empty multi-storey car parks, secluded subway paths, petrol stations - and feature classic horror story motifs, from murderous twins to zombies and aliens. But clowns, he says, are the most effective.
"It's the most scary and creepy thing you can meet at night," he says, adding: "I own the creepy clown voice."
Most of the videos are made in his hometown, but he has also filmed in the United States.
In September 2015 he published a video made in Las Vegas, again featuring a series of menacing clowns.
"That video is my favourite by far," he says.
"It got 1.7 billion views in six months from Facebook posts around the world."
Many social media users have reported being frightened by clowns.
Twitter user Demi Sim was initially unconcerned by the clown craze but has become increasingly worried.
And some people have even reported changing their behaviour because of the threat of the clowns. Katy Erin's comments are typical of much of the reaction that has been seen.
But Matteo does not believe what he does is cruel.
"Taxes are cruel," he says. "I think that a good jog (even if you're running away from a clown) never killed anybody. Everything is under my strict supervision and I spend hours preparing the prank scene to avoid anything going wrong.
"I have people watching the area. Once we've pulled the prank we have people to run after the victim.
"Some people go crazy and I normally say that we were shooting a movie. After they've calmed down I reveal that it was a prank."
Despite this, things do sometimes go wrong.
"I don't harm anyone"
Matteo says that one couple who fell victim to his prank phoned the police. From their point of view, they had just witnessed someone dressed as a clown kill a victim and then chase after them.
Matteo says that he caught up with them to reveal the prank. But by that point, 27 officers in nine cars and two vans were already on the way.
He is not keen on the clown craze that is currently growing around the world.
"The situation is now totally out of control," he says. "I think it probably started as a marketing campaign. People then jumped on the bandwagon for no real purpose and now the worry is that people could be using that bandwagon as a mask to hide criminal acts."
Nonetheless, he recognises that videos such as his could have contributed to the current craze.
"I always write down 'don't try this at home' in the description beneath my videos, but to be honest this stuff is 100% useless.
"But I don't harm anyone and my subscribers know the efforts I go to to make sure it's safe."
Chris Bell, BBC UGC and Social News team