In the text of the prize-winning play by Tulsa native Tracy Letts, Little Charles is said to be sitting next to the woman whom, unknown to the rest of the family, he is in love with. "I wrote this for you," he says. "(He plays, and quietly sings a gentle but quirky love song ...)."

The song chosen for the movie, "Can't Keep it Inside," was one that Cumberbatch (who had some previous piano experience) learned beside GrothOlson in sessions lasting up to 90 minutes at a time.

"That's just him, and it's really gorgeous. He can sing."

She visited the film set and sat down (unexpectedly at a split keyboard organ rather than a piano) to play Cumberbatch's song "for a recording of the song, just in case they needed it," she said. "I was nervous, because it was a bit strange, as I had to play in front of about 30 people, as they asked everyone to be quiet, from all the crew members to the people outside raking leaves, so we could make the recording."

When Cumberbatch sat down at the organ, he acted out his scene and played "Can't Keep it Inside" 14 times  seven times with the camera aimed in one direction, and seven more times with the camera in a different position.

"There was only once that I had to say anything to him, because he was that good," GrothOlson said.