If you're forcing a laugh after a bad joke, the teller probably knows it. Researchers found that people can identify a fake laugh two-thirds of the time: "Quite a few fake laughs sound pretty good, but listeners seem to pay attention to certain acoustic features that are really hard to fake," study author Greg Bryant tells Time. His team recorded real laughter between buddies and laughter forced on command, then played these recordings to subjects and had them guess which was which.
They could tell genuine laughter some three-quarters of the time and fake about two-thirds of the time. It's not the "ha" sound that tips us off to fake laughter, according to Today; it's the breathing sounds in between. It seems there are two vocal systems at play, one emotional and one tied to speech. Real laughter is rooted in the emotional system, which involves more of these breathing sounds. When researchers sped up the recordings, masking these sounds, participants were more likely to believe fake laughs were real. "Laughter is thought to have evolved from labored breathing during physical play. In this way, genuine laughter reveals our animal nature," Bryant says. (Also, this exists: laughing competitions.)