The 'Little Things' hitmakers start to feel nostalgic when they get a whiff of manure whilst they're away touring with their band mates - Zayn Malik, Louis Tomlinson and Harry Styles - because the smell of farm animal poop makes them think of their parents' home.
When asked what smell reminds them of home, Niall, 20, told Cosmopolitan magazine: ''Cow poo.''
Liam, 21, agreed: ''I was going to say the same. We both live close to the countryside. Where I live there are farms and you can always smell...''
Niall added: ''I'm from the lake district of Ireland so there's the smell of cows and sheep and fresh-cut grass.''
Meanwhile, the hunky boy band - who shot to fame after appearing on 'The X Factor' in 2010 - believe they've developed a strong bond, which extends further than just friendship, over the past three years.
Louis, 22, said previously: ''I think 'family' is probably the best way of describing us. It's different to friendship.''
Niall added: ''Yeah, we spend a good time on the road, and, obviously it's so important that we all get along or it won't work.''
Harry explained: ''There could have easily been one person who didn't get along with anyone; who nobody liked, but it wasn't like that.
''The relationship that's grown with these four boys that I didn't even know three years ago is absolutely insane and it's incredible. I'm very lucky that I get to spend so much time with them.''
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