We took Sean and Sarah to see the Sesame Street Live show. (Thanks, Kelly!) The characters were people dancing in puppet costumes with puppet heads. The puppet mouths kept pretty much in sync with the speech and singing and I couldn’t quite figure out how they did it. I saw some guys sitting way out front at some consoles that seemed to control the lights. I was wondering if the entire show was simply a program and the dancers only had to hit their marks while audio and mouth movement all happened automatically or if the dancers were responsible for mouth movement. Anyway, it was impressive. This page has some general info about such costumes.