Martin talks about auditioning for the film in an interview:
“The audition took place with Richard Hunt (he works the Muppet character 'Scooter') and a room full of puppets. After looking over Martin's resume, Hunt asked him to choose a puppet and put it on. Then Hunt proceeded to interview the puppet, not Martin. After a minute he turned to the Cincinnati performer and said, 'You've got it. Thank God you're a real live puppeteer, not an actor!'[1]”