Breaking up is Easy to Do (2) - S11-E15
Continuity mistake: Before the dinner date, Peggy takes a plate of raw meat out of the dishwasher. Bud and Kelly go to help her put it on the stove, but Peggy's plate is now empty and the meat is on another plate already on the stove. Yet strangely, Bud and Kelly take the empty plate from her anyway and put it on the stove next to the other one.
Continuity mistake: In one of the scenes where Bud is forcing Kelly to eat, he tries to feed her cheese whiz but she resists and some of it gets on the side of her mouth. In the very next shot, when Peg runs in, the cheese is no longer on the side of Kelly's mouth.
Chicago Shoe Exchange - S11-E24
Factual error: When Kelly and Jefferson are driving Bud to the chiropractor and puts him on the roof of the car, as they are driving palm trees are lining the road. There are no palm trees in northern Illinois anywhere, let alone lining roads.
Visible crew/equipment: When Al and Jefferson are knocking down the door with Bud, the shadow of the camera is visible on the wall for a second or two.
Breaking up is Easy to Do (2) - S11-E15
Revealing mistake: When Al falls on the bed with the shoe and puts the hole in the water bed, the shoe doesn't hit the bed anywhere near where the water starts to shoot out from.
Visible crew/equipment: When Marcy announces they only have time to grab their most precious personal possessions Kelly notes her own, and in the next shot the boom mic makes a happy appearance at the top of the screen. (00:07:45)
Revealing mistake: Obvious dummies when Al tosses Peg off him on one of their separate beds and when Al falls through the bedroom floor to the den.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.