"There were moments where I'm turning from a human into a reptile, and then turning back from a reptile into a human. Those for me were the most interesting parts to play. I was like, 'OK, how much Lizard am I? How much human am I'," he quipped, reports Flicks and Bits.
"They're really kind of brutalising, emotional, transitional points. And I guess again, [his] drug addict thing, the anticipation and the rush of the becoming."
He continued: "Then there's the awful comedown of becoming human again, with all its frailties and insecurities and doubts and weaknesses - as The Lizard would see them.
"The CGI, obviously, I left to a lot of clever people with computers, but then the transitional stuff I was in the hands of these incredible make-up artists for up to, at its worse, seven hours with four people working on me.
"Which I was very nervous about, because I'm not very good at sitting still for any length of time. But these people are so amazing at what they do, I was kind of transfixed by just watching four great artists create their work on my face. It was kinda cool."