Some performers were not used to lip-syncing to pre-recorded songs, standard procedure for movie musicals. James Brown ended up singing his number live with a recorded backing (the rest of his choir was lip-syncing). John Lee Hooker's performance of "Boom Boom" was recorded live at Chicago's Maxwell Street Market. Aretha Franklin's performance is cut together from many, many takes, using the parts where her lip-syncing was actually in sync.
Carrie Fisher became engaged to Dan Aykroyd during this shoot shortly after he saved her from choking, by applying the Heimlich maneuver.
John Belushi disappeared while filming one of the night scenes. Dan Aykroyd looked around and saw a single house with its lights on. He went to the house and was prepared to identify himself, the movie, and that they were looking for Belushi. Before he could, the homeowner looked at him, smiled and said, "You're here for John Belushi, aren't you?" The homeowner told them Belushi had entered their house, asked if he could have a glass of milk and a sandwich, and then crashed on their couch. Situations like that prompted Aykroyd to affectionately dub Belushi "America's Guest."
John Belushi was nicknamed "The Black Hole" because he went through hundreds of pairs of sunglasses during production. He would do a scene, and then lose the pair before filming the next one.
A world record 103 cars were wrecked during filming. "The Junkman (1982)" broke the record 2 years later, wrecking 150 cars and a plane. That record held for 2 decades, until over 300 cars were wrecked during the filming of "Matrix Reloaded (2003)."
Frank Oz: Just before the Bluesmobile crashes through the Toys"R"Us, a man asks if they have a "Miss Piggy," while holding up a a stuffed Grover toy. This is a nod to Oz, the man who provides both Muppets' voices (a toy version of two more Muppets Oz also performed are visible in the same shot: Animal is sitting next to the counter and Cookie Monster is visible on a shelf in the background). The man with the toy is Gary McLarty, the Stunt Coordinator of this film, and of "Clube dos Cafajestes (1978)."
John Landis: The state trooper driving the second car, the one that shows up after the first car calls for backup, that chases the Bluesmobile through the shopping mall.