If it is not organic this and distilled that, agents are called. Conner Chapman and Shaun Thomas had their own culinary requests during the shoot for The Selfish Giant, though in their case the pleas were far more manageable than goji berries and imported sushi.
"We ended up living off chicken nuggets and chips for six weeks," says Thomas, 16.
The on-set caterers brought them in specially when the boys from Bradford, in the ways of teenagers everywhere, could not warm to the menu offered. Which was? "Salmon, all horrible stuff," jokes Thomas. "Soup," adds 14-year-old Chapman, joining in the collective shudder.
When we meet at the London Film Festival, the new British drama directed by Clio Barnard has been gathering plaudits. Though we don't yet know it, the two will be specially commended in the Best British Newcomer award category when the festival closes.
The winner was Jonathan Asser, the screenwriter behind the highly acclaimed Starred Up, a prison drama helmed by Scots director David Mackenzie and made by Glasgow's Sigma Films. But announcing the commendation for Chapman and Thomas, jury president Amanda Posey said the jury had been "blown away" by the performances of The Selfish Giant duo, calling them "outstanding talents".
Not bad, considering this is their first film. Loosely based on the Oscar Wilde story, The Selfish Giant is set on a council estate in Bradford where Arbor and Swifty (Chapman and Thomas), dealing with troubles at home and school, find a horse and cart and join in the local trade in scrap metal, hoping to get rich quick.
Chapman, who has two sisters and a brother, found out about the auditions from his drama teacher and went along to try out. Amy Hubbard, the casting director, says: "You could have put him on set the next day. He's a natural born actor."
T homas is one of five at home. Like his character in the film he is horse-mad. It was through his involvement in Horsewatch, a scheme run by West Yorkshire Police, that he learned about the picture.
"One of my teachers said Film4 was coming in to do some auditions. I thought it was a documentary or something like that."
Barnard made her name with Arbor, a part-drama, part-documentary about the late playwright, Andrea Dunbar, writer of Rita, Sue And Bob Too. As in Arbor, The Selfish Giant uses a mix of professional actors and newcomers. Chapman and Thomas worked closely with Shameless star Sean Gilder, who plays Kitten, the ironically named, less than cuddly kingpin of the local scrap business.
Thomas admits to nerves before meeting Gilder, and some surprise that he was not Irish, like Paddy Maguire, his Shameless character. "I'm like, 'Eh?'" They soon got over the disconnect, with Gilder giving the pair plenty of invaluable tips. "One piece of advice was to keep saying the line to yourself but say it in a different way to see how you feel it fits best," says Thomas. "He helped us a lot."
The lads helped each other, too, with Thomas teaching Chapman how to ride a horse. The fictional friendship on screen has clearly become a real one.
The toughest scenes for Chapman were the ones where it was cold and the rain machine was on full pelt. For Thomas, it was the scene where he was wearing clothes too small for him and they were irritating his skin. "That was the only thing I didn't like. Apart from the food."
Both know the lives depicted on the screen and recognise the characters. "Where I live it is a lot like you see in the film, people drive round on horses and carts, it's not just children, it's also middle-aged people who have to go on the scrap to earn money because they've got nowt else going on," says Thomas, who comes from Holme Wood. "For a lot of people it's their livelihood."
When they first started the shoot none of their schoolmates knew what they were doing. Then the trailer for the film started appearing in local cinemas and they were rumbled.
"You get a few people that get jealous of it, but apart from that it was just normal," says Chapman. Thomas had good natured teasing, with one of his mates telling him he was going from "Holme Wood to Hollywood".
Earlier in the year the two went to Cannes. "Quality," sums up Thomas. Before London, their favourite festival had been Dinard in France. "It was more relaxed and low key," says Thomas. "You could do a lot more, speak to more people. The only thing that was hard about it was trying to speak French." The food, alas, was a disappointment again. "We went for this gala meal and it was all fish and stuff."
They now handle interviews like pros, noting that journalists all tend to ask the same questions. As for being away from home and staying in many starred hotels, it's all part of the craic. With a daily allowance, room service is their oyster.
"We can spend £100 on what we want," says Thomas, "and we're only here until tomorrow."
They are hoping to stick around a lot longer than that in acting, though. Now signed with an agent, auditions have been lined up, one of them to play brothers. On-set caterers, get ready.
Glasgow Film Theatre, Filmhouse, Edinburgh, and DCA, Dundee, from tomorrow