During filming, Peter Mayhew actually spoke English dialogue for Chewbacca so that his character's conversations with the actors would seem more natural. In post production; his dialogue was dubbed into what we see now Chewie's growls and barks. A clip of Chewbacca's voice before dubbing in the Death Star control room scene is shown on the documentary included in the new 2004 DVD release.
According to Lucasfilm president Kathleen Kennedy, when Harrison Ford and Peter Mayhew set foot in the Millennium Falcon set, every person on set was stunned. Kennedy claims that there must have been 200 people who were completely quiet, due to the iconic presence of Ford and Mayhew back on Han Solo's ship.