Bob says he wanted to make the movie look like the oil paintings in the book. To do so, Tom had 194 tiny plastic jewels glued all over his body. When he acted out his scenes against a blue screen, infrared cameras guided by the jewels captured his every move. Animators then used the data to create a computer-generated shell and wrapped digital "skin" around that shell to create the five different characters Tom plays in the movie.
Tom: At one point, Bob said, "I think you should play everybody in this movie. I think you should even play all the elves." I said, "Bob, I can't."
Bob: He's my favorite actor. I'll do everything with this guy!