I had a childhood friend, who often started laughing and his laughter was so contagious, so I also laughted. He was starting to laugh just because he knew I would also start to laugh. And I laughed because I knew he expects me to laugh and I wouldn’t be able to stop myself from laughing. And vice versa recursively. The whole situation was so absurd, so we were continuing to laugh just because from the outside it looked like we started to laugh for no reason.