Niall Horan has a set routine for each of his solo live performances due to his battle with obsessive compulsive disorder (OCD).
The Slow Hands star previously revealed that he had a mild version of the mental condition, in which sufferers feel the need to check things or perform certain routines repeatedly, and he has opened up about how they affect his live shows to German magazine ZEIT LEO.
"I have one fixed sequence. I always have to sing in the same order, move and so on," he said. "I'll basically do everything immediately, otherwise I'll get nervous quickly. That's why in school I learned to start studying for tests very early. Otherwise I'd be afraid of the pressure."
The One Direction singer, who is currently on his Flicker World Tour, also went on describe another one of his "ticks".
"I feel like I have to do things in a certain way. For example, if I have a burger with chips on my plate, I always have to eat the chips first and only pick up the burger at the very end," he revealed.
The 24-year-old admitted his ticks and his interest in music over sport meant he wasn't very popular at school, but he has now learned to accept his condition, thanks to being around more understanding people.
"I live with them (ticks) and they're mine no matter what others think about it," he continued. "I'm just like - what the hell! Fortunately, I now have enough people around me who understand me."
Niall knows he's not like "most normal people", but he's realised a lot of musicians are similar to him, if not worse.
"Some have much stronger ticks than I do. A friend of mine has to, for example, always exactly do things three times when he washes his hands: soap three times, rinse three times, dry off three times," he revealed.