Smith, 43, who reprises his role as Agent J in the forthcoming sequel, said that his biggest fear was that his already large features would be the main focal point of each scene, reported Contactmusic
"This is my first time making a movie in 3D, I was just happy my ears didn't take over the whole frame. That was my big concern, that in 3D these things would be exponential!," he said.
Smith and his co-stars Josh Brolin and Tommy Lee Jones used a lot of ad-libbing when they worked together, and the actor said they spent time preparing what they wanted to say.
"We do spend a lot of time before we get on the set coming up with things. When we're working a scene we will ad-lib the three or four days before we're actually in a scene. Coming up with things, trying things, and we'll have four or five different options of things we want to try."