A.V. Club have a feature called "Random Roles," in which they "talk to actors about the characters who defined their careers." Today they're talking to Elijah Wood, and one of the films they ask about is Eternal Sunshine.
The opportunity to work with Michel Gondry and Charlie Kaufman was an absolute dream. It’s literally a movie that I would’ve wanted to do anything to be a part of any aspect of it. [Laughs.] I’ve always loved Kaufman’s writing, and I’ve been a major fan of Michel’s work in music videos as well as the movie he first collaborated with Charlie on, Human Nature.
I can remember specifically that there’s a sequence in the movie where Jim [Carrey] is moving from memory to memory, and he leaves a house, walks down a hall, walks into a doctor’s office, sees himself talking to the doctor, and then runs out of the office. Well, that was all one shot, and we did it—I think we did maybe 16 takes, which is actually not bad considering how complicated that was. And it was one of those moments that was a real uniter of the crew and everyone, this sense of, “We can literally watch a playback and see it all happen in camera,” and it was so extraordinary. I remember the sort of celebratory feel of everybody at having accomplished that, and also, I think, a realization of the kind of movie we were making and a really obvious realization of Michel’s vision. It was really special. It was awesome. (Source)
Such a great movie.