Think of the most hilarious video you’ve ever seen on the internet. Why is it so funny?

As a researcher who investigates some of the potential side effects of humor, I spend a fair bit of time verifying the funniness of the jokes, photos and videos we present to participants in our studies. Quantifying the perception of humor is paramount in ensuring our findings are valid and reliable. We often rely on pretesting — that is, trying out jokes and other potential stimuli on different samples of people — to give us a sense of whether they might work in our studies.

To make predictions on how our funny materials will be perceived by study subjects, we also turn to a growing body of humor theories that speculate on why and when certain situations are considered funny. From ancient Greece to today, many thinkers from around the world have yearned to understand what makes us laugh. Whether their reasons for studying humor were strategic (like some of Plato’s thoughts on using humor to manipulate people’s political views) or simply inquisitive, their insights have been crucial to the development of humor research today.

Take the following video as an example of a funny stimulus one might use in humor research:

Man vs. Moose in Sweden.

To summarize: A man and his female companion are enjoying a pleasant day observing a moose in one of Sweden’s forests. The woman makes a sudden movement, causing the moose to charge the couple. The man stands his ground, causing the moose to stop in his tracks. After a few feints with a large stick and several caveman-ish grunts by the man, the defeated moose retreats while the man proclaims his victory (with more grunting).

The clip has been viewed on YouTube almost three million times, and the comments make it clear that many folks who watch it are LOLing. But why is this funny?