"It forces you to stay in shape because you never know when you're going to be asked to get naked," he said of the HBO hit. "What scares me is not knowing when that scene is going to be shot. Sometimes they'll say, 'Oh, you have to be naked in three days.' Because we're all so naked we all sort of hold each other's hands and jump off the cliff together. They are very respectful and I'm never fully, fully, fully nude."