Continuity mistake: Marcy's floral headpiece falls off during the backyard wedding scene, then, in the next shot, after she hits Al with her flowers, it appears on her head again. (00:18:30)
Visible crew/equipment: Right after Jefferson walks out after saying what he was in jail for, when they are showing Bud and Al, you see a large head shadow go across Bud's leg from left to right.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.