The act of touching a robot in an “intimate” spot results in uncomfortable feelings in humans, a surprising new study finds.

And it’s a discovery that could change how future toys or even robot companions are designed. As the sophistication of robots increases, more interactions between humans and robots has pushed researchers to better understand both the benefits and the drawbacks of the interactions, according to an International Communication Association statement.

It also shows that touch is a powerful form of communication, perhaps even more so than gestures and speech, which could affect how much importance is placed on that as a communication option.

Researchers experimented with the small humanoid NAO robot from Aldebaran Robotics based in Paris, which is capable of recognizing faces and objects and can express emotions. They programmed the robot to ask volunteers to touch 13 parts of its body as they were fitted with sensors to measure electrical conductivity — a way to determine how much sweating was happening, and thus providing clues on their emotional response.

When they were asked to touch the crotch, buttocks, or eyes of the robot, there were much stronger emotional responses in the 10 volunteers compared to touching the hands or neck. Participants also were more hesitant to touch these areas and more slowly did so in the study.

“Our work shows that robots are a new form of media that is particularly powerful. It shows that people respond to robots in a primitive, social way,” Jamy Li, one of the researchers on the study from Stanford University, said in the statement. “Social conventions regarding touching someone else’s private parts apply to a robot’s body parts as well. This research has implications for both robot design and theory of artificial systems.”

The statement adds: “A large body of research in communication shows how touch is used as a social ‘glue’ between people – building relationships and influencing trust. Not as much is known about touch between a person and a robot. Touch has been underexamined compared to other aspects of robots, such as its appearance and shape.”