Laughter is contagious, but in this Berlin subway car, it’s a virulent disease. Watch as it infects every single person on the train below:

Just what are they laughing at?

Nothing, it turns out. Laughter for laughter’s sake is the goal of the Berlin Laughter Project, which orchestrated the event in a sort of flash-mob-meets-performance-art event. The absurdity of the laughter puts everyone on the train in stitches, elevating a dreary commute to an endorphin-boosting ride that leaves its passengers — and the video’s 1 million-plus viewers — grinning.

For the BLP, the laughter isn’t just for fun — they consider it therapeutic, “a powerful antidote to stress, pain and conflict.” And as a way to cheer people up on their commute. It’s a lot funnier (and warmer) than the annual pants-off Metro ride.

People take part in the 10th annual No Pants Subway Ride in New York. The event, organized by Improv Everywhere, involves participants who strip down to their underwear as they go about their normal routine. (Jessica Rinaldi/Reuters)