Emma Thompson gave a surprising performance in Saving Mr Banks, Jason Schwartzman has revealed.
"I think that Emma is incredible because she is so funny and so engaging, and yet so tough. She's both funny and bittersweet. She does it all," Jason said at the recent Disney Expo.
The actor, who plays composer Richard M Sherman in the film, added: "It's amazing to work with her every day and then to see it on screen, I'm noticing things I never did before. It's like sleight-of-hand in magic. I was right there, and I still didn't see it."
BJ Novak, who portrays Richard's songwriting brother Robert, revealed Emma did the role justice.
"The amazing thing about Emma's performance in this movie is that she's the bad guy to everyone else. She doesn't want Mary Poppins to be made, she doesn't want it to have music, she doesn't want it to be funny. She doesn't want all these people to have their way," he said.
"And yet, you love her, you're fascinated by her and you want to know why she is the way she is. That's a great performance."
Jason admitted that while he had seen the Mary Poppins film, he hadn't read the books until he signed on for the movie.
"I didn't read the books until this movie came along. They're very interesting and now they're just a part of our lives in an even deeper way," he said.
Saving Mr Banks, which will close the London Film Festival on October 20, will be released on January 17, 2014.