Brie Larson, right, and Jacob Tremblay appear in a scene from “Room.” (George Kraychyk/A24 Films via AP)

(This post contains spoilers about the plot of “Room.”)

If you saw “Room,” a horrifying drama about a woman (Ma) and her young son (Jack) locked in a shed by a predator for years before planning a daunting escape, you may be wondering — isn’t the kid who played Jack completely traumatized by starring in this movie?!

As it turns out: no, not at all. For Jack, the shed (known as Room) is the only world he’s ever known, so his nightmarish living conditions actually seem completely normal. He’s still a regular kid — Room might be small, but he draws pictures, watches TV, reads books, plays games with his mom. Jacob Tremblay, the 8-year-old actor who played Jack, approached the film in much the same way.

[Why ‘Room’ could be the indie version of ‘Gone Girl’]

Brie Larson, who stars as Ma, recently took questions in Washington after a screening of “Room” and said everyone is worried about Jacob’s well-being. But they really shouldn’t be.

“He never knew that anything difficult was going on. He only knows as much as Jack knows, and the way that he sees the world is that everything’s great,” Larson, 26, explained. It was rough for her to psychologically get into character, given that Ma has Jack after she’s raped by her captor. Yet all Jacob knew was that he got to play make-believe every day on a movie set.

Larson recalls rehearsal for one upsetting scene where Ma devises a plan to have Jack pretend to be dead so her captor, Old Nick, will have to take him out of the shed. Ma decides to roll Jack up in a rug so Old Nick can’t see him. And when he throws the rug (known as just Rug) into the back of his truck to go bury the body, Jack will wiggle free, jump out of the truck and get help.

“I have an incredible video of the first time we rehearsed rolling him up in Rug. And I’m weeping, [director Lenny Abrahamson] is weeping, because we’re realizing the ridiculous thing that we’re about to do and how moving this whole sequence is,” Larson recalled. “And Jacob was laughing. Hysterically laughing. He thought it was the funniest, most ridiculous thing that a person could do.”

She said that Jacob acted like the whole thing was one big game. This continued when he was stuffed in the back of the truck by Old Nick, wrapped in the rug.

“All the stuff in the back of the truck, we watched that and we’re all going ‘Oh no!’ That was two days of stunt work. For an 8-year-old, that’s a dream come true,” Larson explained. “He was like, ‘I’m Tom Cruise now!’ ”

“I know people do worry about Jacob,” she continued. “But he loved every second of it.  And it wasn’t just this downer set where we were all, like, trying to keep it together. We laughed a lot, we had a great time the whole time, and he really loved it.”

“Room” is already considered a favorite for award show season, with prognosticators betting that Larson is a lock for an Oscar nomination. (Jacob is also getting some whispers as a potential best supporting actor nominee, though you never know with child stars.) So what did he think of the final product? Larson laughed recalling the night of the film premiere.

“All of us were sort of nervous, because he didn’t really know what the whole movie was either,” Larson said. “Afterwards, his mom was like, ‘So Jacob, what did you think of the movie?’ He was like, ‘Yeah, it’s good — but it’s no ‘Avengers.’ ”

Read more:

REVIEW | ‘Room’ takes the parental bond to harrowing and tender extremes

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