Producers are so worried about talent walking off and getting injured, stars are often allocated personal minders, who accompany them everywhere.
And the Across The Universe star found the practice particularly annoying on the set of his new film One Day.
He explains, "I was heavily chaperoned with people with walkie talkies saying, 'Yeah, he's just going to the toilet, we can hear him come out now!' They wouldn't lose me or (co-star) Anne Hathaway.
"That's always the weirdest thing about being in a film - if you go to the toilet, there's always someone waiting for you as you come out. I think it's called a 10-1, or something: 'Jim's just come out of a 10-1'. It sounds like a military operation."