Wiggle your fingers in someone’s armpits or along the bottoms of their feet and you’ll likely elicit laughter, squirming and shrieking—no matter where the person is from.

Scientists have discovered that people from distinct cultural backgrounds are ticklish in many of the same spots on their bodies. In addition to the armpits and soles of the feet, the belly and the neck consistently rank as some of the most ticklish body parts across cultures, scientists report in a study published August 10 in the journal Nature Human Behaviour. The findings could help researchers unravel why this strange sensation evolved.

Ticklishness is a nearly universal human sensation—and one that we share with rats, meerkats and great apes—yet scientists know surprisingly little about it. Researchers recognize two types of tickling: knismesis, a light, feather-like sensation that usually doesn’t provoke laughter, and gargalesis, which is caused by firm, repetitive touches that typically elicit giggling and movement.

Until now, research on tickling has been largely focused on knismesis because of its similarity to itchiness, a symptom of many medical conditions. Gargalesis, meanwhile, has remained “really a very poorly understood sensation,” Michael Brecht, a neuroscientist at Humboldt University of Berlin who was not involved with the study, tells Nature’s Claire Ainsworth.

In the new study, a research duo set out to understand some of the basics about gargalesis. They recruited 448 participants divided equally among three cultural backgrounds: Chinese, Dutch and Greek. Each completed a survey about tickling and created a body map of their most ticklish spots, along with maps for other sensations, including pain, pleasure and touch sensitivity.

The data yielded “remarkably similar patterns regardless of where participants came from,” study co-author Konstantina Kilteni, a neuroscientist at Radboud University in the Netherlands, says in a statement.

More than 98 percent of participants had been tickled, and more than 95 percent had tickled others, suggesting that tickling is a widespread behavior. While that might not sound surprising, certain behaviors involving touch, like hugging, can vary depending on cultural background. Additionally, more than 70 percent of respondents rated themselves as moderately to very ticklish.

The survey data also revealed an age-related difference in the enjoyment of tickling: 42 percent of respondents said they enjoyed being tickled as children, while just 35 percent said they enjoyed being tickled as adults.

Most of the participants felt neutral about the experience of being tickled—it wasn’t enjoyable or unpleasant. However, more than a quarter found it to be unpleasant.

The body maps not only revealed cross-cultural ticklish hot spots, but they also allowed researchers to test several possible theories about why some body parts seem to be more ticklish than others.

They ruled out a few altogether, including the idea that the most ticklish areas are those with the thinnest skin. If that were true, areas like the eyelids and lips should have shown up in the maps. The most ticklish regions also didn’t seem to line up with the most vulnerable parts of the body, nor the areas where touch feels most pleasurable, the researchers found.

None of the proposals examined by the researchers fully solved the ticklishness puzzle on its own. But one seems partly to explain why ticklishness varies across the body: The idea, put forth by British naturalist Charles Darwin, posits that the most ticklish areas are those that don’t get touched very often.

However, “more research is needed before we can fully explain the phenomenon,” Kilteni says in the statement.

Fun fact: Tickle bot

Some of that research is already underway at Kilteni’s Touch & Tickle Lab, where participants willingly take off their socks and shoes to have their bare feet tickled by a robot named Hektor. During the process, their facial expressions, heart rate, brain activity and other reactions are tracked.

With ongoing and future studies, the scientists hope to deepen their knowledge of tickling, including its evolutionary origins and its biological and social functions. Knismesis might have evolved as a defense mechanism, a sensation that helps us feel—and flick off—potentially dangerous pests crawling on our skin. However, the story of gargalesis is a bit murkier.

“It is one of the first things that makes us laugh as infants, and has been proposed to be an important social activity—first between caregivers and infants, later between other close family members and friends,” Anina Rich, a neuroscientist at Macquarie University in Australia who was not involved with the study, writes for the Conversation. “It has also been proposed that being ticklish trains us to protect our vulnerable parts or acts like a reflex that moves us away from a potentially damaging stimulus.”

Research on tickling might also help scientists better understand certain neurodevelopmental or psychological conditions, such as autism and schizophrenia, which seem to affect how people process and perceive physical sensations, Kilteni wrote for Scientific American in March.

“Behind every giggle, there’s a fascinating bit of neuroscience waiting to be discovered,” she added.