Lardass started it in Stand By Me (1986). Mr. Creostote got it going in The Meaning of Life (1983). And many of us have seen the knock-on-effect of one person spewing at a party, and the rest running to the bathroom to follow suit. The Vomino Effect begins when one person has a chuck, causing the people around them become nauseated, often to the point of vomiting themselves. But why is it that vomit goes viral?

This behavior is thought to have evolved back to when we were primates browsing in the wild, eating in small social groups, and basically playing a risky game of trial and error with our surroundings to see which foods meant 🙂 and which meant :(. In this group dynamic, being attuned to your neighbour’s vomit meant picking up a survival cue that could spell the difference between life and death; if someone nearby ate a poison berry, or some rotten meat, or a bad egg, it was likely you’d eaten it too, so it would be advantageous to vomit as a just-in-case. This means that being sensitive to other people’s up-chuck, far from making you a weakling, was an adaptation to help you survive.

Professor Cox at the University of Salford’s Acoustic Research Centre suggests that “we are pre-programmed to be repulsed by horrible things such as vomiting, as it is fundamental to staying alive to avoid nasty stuff”. This is why the smell, sight, and sound of someone vomiting is so yucky; in fact, in an online study of the “most horrible sounds”, hearing a call to Ruth on the great white telephone (a.k.a someone vomiting in the loo) came in at number 1. If you’re keen to add your ears to this experiment, you can access this hearing survey here.

But while most normal people* aren’t vomit fans, not all vomit-responses were created equal. “If you and I and 10 other people are sitting in a room and one person vomits, I wouldn’t say everybody would automatically vomit,” says Dr. Paul Kassab of Seattle’s Virginia Mason Medical Center. “One person may turn their head, another may try to help; another may gag or vomit because of the smell. It’s something you can’t predict, although you can predict it for yourself by knowing your own sensitivities.” Kassab thought that vomiting was controlled by a “variable degree of nature and nurture”, meaning the severity of your response really depends on who you are. People were more developed senses of smell are often quicker to lose their breakfasts, whereas those a who have a solid background tolerance of spew (like nurses and parents) can better control their gag-reflexes. This shows that our propensity to vomit can change according to our environment and past experience.

So if you’re ever caught in the melee of a group-vomit, remember that you’re seeing evolution in action and witnessing one of the human body’s many ingenious ways of protecting itself. Even if it does happen all over your parents’ good towels.

*This doesn’t apply to emetophiliacs who are, it turns out, not normal people.