We all know those people who, at weddings or clubs, stand there just off the dance floor, looking around helplessly while everyone boogies down to the music. “I can’t dance,” they might say. Well, in some cases, that might actually be true.

In a November 2014 study, researchers at McGill University found that although most individuals have a natural sensoral ability to tap along to a beat, or sway their hips to the rhythm of the music, some people just can’t. And their condition has a name: beat deafness.Here’s how it works (or doesn’t): When you clap or dance, or even walk or play an instrument, your body is using complex external signals and syncronizing your actions with them. Even if a regular, expected beat is not noticable in a song, your body is able to process the signal and maintain a constant rhythm with it. Beat-tracking, the researchers write, is explained by the theoretical idea of a pulse— a perceived regular beat generated by an internal oscillation. This is what experts think form the foundation of internal timekeeping mechanisms.When we listen to music, this internal oscillator adapts to respond to the stimulus. When there’s something wonky with your internal oscillator, you can’t clap to the beat or march in line with everyone else. You literally march to the beat of your own drum.

In the study, the researchers asked two beat-deaf subjects to tap along to a metronome, which threw in a few irregular beat patterns to throw off the subjects. “Both beat-deaf cases exhibited failures in error correction in response to the perturbation task while exhibiting normal spontaneous motor tempi (in the absence of an auditory stimulus), supporting a deficit specific to perception–action coupling,” the researchers wrote. In English: the beat-deaf people were unable to pick up the regular beat after an interruption. When tasked to tap along to the normal metronome, they were less precise than the control group. However, they were able to create a beat on their own without a stimulus — which means the problem arises when their brain is trying to process an external sound and mimic it.

Caroline Palmer, psychology professor at McGill, noted that beat-deafness is a pretty rare disorder. Scientists aren’t exactly sure yet as to why beat-deafness happens, but they’re pretty sure it’s not a conscious thing; rather, a reaction a small percentage of people have when engaging with sound. (As for the rest of us? Blame alcohol.)Check out what else Palmer has to say in the video below.