When Falfa's Chevy flips over, we can see that it has no fuel tank at all in it. However, in the next shot the car now has a visible fuel tank, and it explodes.
When Terry is being introduced, he drives up on his scooter, and has quite a bit of trouble parking it. This is because Charles Martin Smith actually didn't know how to drive a stick shift. The small accident he has is real, you can see him crash, look up towards the camera (at Lucas), and continue the scene. Lucas motioned for him to continue, because the crash looked so interesting.