Lee said, "The final thing he has to fight for is his sanity. ... We're going to a state of mind that's very unusual. Let's say he's with God. So yeah, I didn't let anybody talk to him. He had to live in solitude."
Lee said Sharma should have been nominated for an Academy Award.
"People forgot how naturally he blended into the movie. He is Pi. To me, that's the beauty. That's the purest form of acting. It's precious."
Lee confirmed that, because the computer-generated tiger looks so real, he had to prove to the Indian government that he hadn't abused a tiger.
"The tiger's emaciated, and Pi puts him on his lap," Lee said. "You cannot do that to a real tiger. ... We didn't drug the tiger or anything." It was all computer-generated imagery, he said.
"It's very hard to imitate God's work," Lee said with a laugh, "whether it's a tiger or the water, it's impossible. We try to get as close as we can."
How much does Lee want the Academy Award for Best Picture?
"I want it, because I'm the captain of the ship, you know, for the 3,000 people [in the credits]. For what the movie stands for. There is no star. It's an unusual movie. [For] what it meant to the world. For the people who spent four years of their life devoted to this grand illusion."
Watch the full story, including Cynthia McFadden's interview with Ang Lee, on "Nightline" TONIGHT at 12:35 a.m. ET