Sometimes crazy things happen on the subway.
A busker on the London tube recently went viral when his captive audience spontaneously burst into a conga line.
Wilfy Williams is the performer that caused people to throw a little subway dance party.
"It's not that big of a deal having crowds singing and dancing like that, it happens quite a lot, but I think why it went viral is they started doing the conga," Williams told the PA Media news agency. "That's bizarre isn't it? I've never seen a conga before."
The moment was captured on video by Helena Whittle as she was heading home.
"I came down the escalator and I could hear him," she told PA.
"There was a group of Spanish young people, boys and girls, four or five of them, who were watching him so I stayed with them. They got the whole party going because they were clapping and singing along."
More people joined as Williams sang "Scream and Shout".
"I guess it was the song he was singing and he was getting a response from the audience," she said.
"It just happened to be that so many people came down and all heard him, one thing leads to another, you see people dancing, suddenly you're not too shy to dance as well – maybe the time of day helps as well, being half past 11 at night, happy hour, weekend starting."
Whittle shared the video with Williams and some of the people who'd been dancing in the crowd as the passengers dispersed, as well as sharing it on Facebook.
The conga broke out as Wilfy Williams played Twist And Shout (Helena Whittle)
Her own post on Facebook has been viewed more than 800,000 times, while a version posted on Twitter has received more than three million views.
"I've been waiting for this to happen," Williams, who has been busking for around 10 years, said.
"I've seen all these audiences filming me and I'm like 'one day this is going to go viral' and I've just been waiting. I think it was the conga that did it."
Williams said he believes "the political environment" means people are looking for things to make them smile. His new song, "A New Beginning" was released in December.
The internet loves this minute of pure happiness.
"People are up and down and then all of a sudden there's joy, and we all just need a bit of joy in the world," Williams said.
"And that is a musician's job, or a comedian's job, or any artist, is to bring a bit of joy."