Only recently described by science, the mysterious mushrooms are found in different parts of the world, but they give people the same exact visions.

Every year, doctors at a hospital in the Yunnan Province of China brace themselves for an influx of people with an unusual complaint. The patients come with a strikingly odd symptom: visions of pint-sized, elf-like figures – marching under doors, crawling up walls and clinging to furniture.

The hospital treats hundreds of these cases every year. All share a common culprit: Lanmaoa asiatica, a type of mushroom that forms symbiotic relationships with pine trees in nearby forests and is a locally popular food, known for its savory, umami-packed flavor. In Yunnan, L. asiatica is sold in markets, it appears on restaurant menus and is served at home during peak mushroom season between June and August.

One must be careful to cook it thoroughly, though, otherwise the hallucinations will set in.

"At a mushroom hot pot restaurant there, the server set a timer for 15 minutes and warned us, 'Don't eat it until the timer goes off or you might see little people,'" says Colin Domnauer, a doctoral candidate in biology at the University of Utah and the Natural History Museum of Utah, who is studying L. asiatica. "It seems like very common knowledge in the culture there."