Continuity mistake: When Kelly is at the grill, right after being called a "dullard" by Bud, Kelly grabs Bud's wrist with her left hand. As we pan out on the exact same scene, her hand is nowhere near his wrist.
Continuity mistake: Al takes the kids camping. When he leaves the house, his shirt is light blue. When he comes out from the bushes in the woods, it's dark blue with red stripes.
Continuity mistake: A lady agrees to buy some of Peg's red hair. It shows the lady with two baggies with red hair in them, but at the end of the episode we see that they used Buck's hair, which is far from being red in color, or anything like human hair.
Continuity mistake: When Kelly blows up the car near the end, when they show the car before it explodes, you see someone walking on the right side behind the car. Half a second later the car explodes and now someone is walking by the building on the left side of the screen. There wasn't anyone there before.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.