Billie Eilish spoke about the subject during the season four premiere of My Guest Needs No Introduction with David Letterman. Tourette syndrome is a neurological disorder that causes people to make unintended sounds, words and body movements, called tics." The artist told Letterman, "If you film me for long enough, you're going to see lots of tics." Eilish said people don't always understand when it happens. "The most common way people react is, they laugh because they think I'm trying to be funny," she said. However, the Grammy winner noted that she's "happy talking about it" and thanked Letterman for asking. Eilish explained she was diagnosed with Tourette syndrome when she was 11 and had small tics as a child. "The main tics that I do constantly all day are, I wiggle my ear back and forth and raise my eyebrow and click my jaw, flex my arm and flex these muscles. These are things you would never notice, if you're having a conversation with me. But for me, they're very exhausting but now I feel like it's a part of me. So now, I'm pretty confident in it."