Continuity mistake: After the cop car hits the Winnebago, we see the car's back window is completely gone in two separate shots. However, when the camera angle does a close up on the car, we see a cop pushing out the rear windshield which was simply not there the shot before.
Continuity mistake: At Chez Paul, when Jake and Elwood first meet up with Mr. Fabulous, who is talking on the phone, there is a shot of them walking down the hallway towards him and you can see that Mr. Fabulous is looking right at the two brothers. In the next shot, his head is down and he then looks up at Jake and Elwood.
Answer: It's 'Can't Turn You Loose,' often refered to as the Blues Brothers Theme.
rabid anarchist
Also done much earlier by Otis Redding.