Woody Harrelson terrified co-star Mark Ruffalo when he hypnotised him into seeing the world as green.
Harrelson learnt the art of hypnosis from Irish mentalist Keith Barry when he worked as a consultant on movie Now You See Me and its sequel, due this summer.
But Barry admitted he had "created a beast" in Harrelson who has taken to using his mind-bending skills on everyone from the Hulk actor to restaurant waitresses.
He explained: "Mark Ruffalo challenged (Woody) to hypnotise him. I'm sitting here in New Orleans in a restaurant, thinking, 'This will be interesting', and he did, he hypnotised him.
"Because Mark was an actor, I was wondering if he was going to play along but he didn't. He went under.
"Woody didn't know what to do so he said, 'You can only see the colour green.'
"Mark woke up and freaked out because everything appeared green to him."
He added: "Woody, I think I've created a bit of a beast there.
"He brought me to the Chiltern Firehouse and he was hypnotising waitresses and I'm like, 'Jesus, Woody, sit down, cool your jets.'"
Harrelson was not the only quick learner on set.
"Dave Franco, I could put him up there with the best card throwers in the world. Not the best sleight of hand but he could take a card and fire it over there and stick it into an apple.
"If he kept training at it, he could definitely break a Guinness World Record, he's that good."
Barry is putting his expert hypnotism skills on show in the second series of You're Back In The Room, where members of the public are put under Barry's spell to do silly things for cash.
This series will see contestants convinced they are delivering host Phillip Schofield's best man speech, travelling on the world's tallest roller-coaster and fighting a fire engulfing the audience that desperately needs dousing, all from the comfort of a TV studio.
Schofield has yet to be put under Barry's spell, but he has his eye on a bigger target: Simon Cowell.
"Simon Cowell would be interesting to really be hypnotised instead of a dog looking at him and his head falling down (as happened on Britain's Got Talent). I think to get Simon Cowell out his comfort zone is interesting."
The show celebrated its first baby in September after a previous contestant who confided in Barry that she had trouble conceiving said she relaxed for the first time in 18 months after Barry's post-filming "de-frag process", went home and got pregnant that night.
But does he ever use his skills for evil?
"I'm not saying I do evil things, I'm just saying if a cop stops me when I'm speeding sometimes, not all the time, I might get out of that ticket.
"Let's just say I don't have any points on my licence in Ireland and I drive relatively quickly," he laughed.
:: You're Back In The Room begins on ITV at 8.30pm.
