So Dr. Kupfer together with Sonia Alas and Tiffany Hwang, then students at UCLA, through YouTube. They watched and debated for hours to choose the most hideous footage possible. Many options were too weak, such as taking pictures of “slightly moldy food,” said Dr. Copper. “We wanted feces, we wanted some kind of infection,” he clarified.

Dr. Copper’s dream came true. The latest ectoparasite clips featured a flea-riddled kitten, a nightmarish bed bug infestation, and a beauty shot of a blood-sucking mosquito. The latest pathogen clips included meat pulsing from maggots, an infected arm lesion that oozes pus – Dr. Fessler called it the “pus volcano” – and a lump of ear wax as dark as an asteroid.

The meat was Dr. Kupfer’s own creation; Unable to find an appropriately disgusting video of rotten food, he left a piece of meat in his garden for two weeks and returned when it “looked grossly disgusting,” he said.

The video that the researchers found most disgusting – in the newspaper’s additional information entitled “Dirty Festival Toilets” – has since been removed from YouTube. This is perhaps the best. I tried to watch every video used in the experiment. I didn’t throw up, but my heart was palpitations and I had to sit in my bathroom with the lights off for a few minutes until I could no longer see the pus volcano. Missing the dirty festival toilets seemed like an act of self-care.

The researchers conducted essentially the same experiment three times, twice in the United States and once in China, and interviewed more than 1,000 people in total. In all three surveys, the participants showed clear reactions to the ectoparasite videos compared to the pathogen videos. When observing ectoparasites, participants reported more itching and scratching, which theoretically protected the skin surface from danger. And when observing pathogens, participants reported more nausea and vomiting.

The researchers plan to expand this project internationally to see how the disgust responses of ectoparasites vary in different countries and in different languages. Understanding the nuances of disgust could affect our understanding of disorders such as delusional parasitosis, the mistaken belief that parasites have invaded the body.

Bunmi O. Olatunji, a psychologist at Vanderbilt University who was not involved in the research, said he thought the results of the new paper were too preliminary to draw conclusions about clinical conditions. But it offers “interesting ways to think about the mechanism by which disgust can contribute to the development and maintenance of a skin-picking disorder”.