Niall Horan suffers from loud flatulence.
The One Direction hunk gets bad wind and is constantly letting one rip in front of the other boys, who have become "immune" to his loud bottom trumpets.
Zayn Malik laughed: "He doesn't like me telling people, but Niall farts the most out of everyone! The thing with him is that they're really noisy, but they don't actually smell that bad.
"They're kind of bearable - or I might have become immune to them! It's just like really loud air coming out of his bum."
The childish amusement the group - also comprised of Harry Styles, Louis Tomlinson and Liam Payne - get from Niall's farts is reflective of their general attitudes.
The 'Kiss You' hitmakers are big kids at heart and love nothing more than messing around with lightsabres backstage at that shows.
Zayn added to Top of the Pops magazine: "We're all big kids when it comes to toys and stuff. We have big lightsabers, a few toys and an Iron Man mask.
"We just like messing about with toys, but I think we're past the teddy bear stage now, haha! But lightsabers are cool."