An aisle over in the grocery store, someone lets out a nasty cough, and you shudder. “That person sounds really sick,” you think as you head in the opposite direction.

A new study may prompt you to think again. Humans can’t hear a difference between the cough of someone with an infection and someone with a mere tickle in the throat, researchers report June 10 in Proceedings of the Royal Society B

People can fight infections off with the immune system, but that can take a lot of energy and doesn’t always work, says Nick Michalak, a social psychologist at the University of Michigan in Ann Arbor. “Many organisms, including humans, have developed prophylactic behaviors to prevent pathogens from [causing infection] in the first place,” he says, like being grossed out by possibly infectious material like feces or snot.

While there’s evidence that people can somewhat accurately suss out another’s infection by sight and smell, Michalak says sound was relatively unexplored.

He and his colleagues played short audio clips of coughing from apparently sick and healthy people collated from YouTube for over 200 volunteers, asking whether each cough was from someone who was ill or not. Despite expressing confidence in their abilities, participants did no better than a coin flip in distinguishing between the two types of coughs.

Read the full article at Science News.