Syncro-Vox

Syncro-Vox is an animation technique by which static images of character's faces have holes cut out where their mouths would be so the hole can be filled with a live actor's mouth to move for the dialogue. It has most famously been used in the series Clutch Cargo, which was featured in the Butch Coolidge childhood flashback scene in Pulp Fiction. More recently, it is the process used in the "Celebrity Lips" segments on Late Night with Conan O'Brien, in which Conan "interviews" the President, world leaders and other celebrities while one of his writers (usually Robert Smigel) provides the celebrity's voice.