On the bleacher, some people behind Lois and Peter disappear, then reappear seconds later.
The bite is missing from Peter's hot dog when he throws it at Meg.
When Peter is driving the car that looks like a penis, there is a white line in the middle of the road. When the shot shows the approaching tunnel, the line is gone. In the following shot, the line is there again.
When the family is eating dinner, in the first shot of Stewie, there is a pile of some off-white food on his plate. In all subsequent shots, the pile is green.
When Peter is shooting his shotgun, the door to the house behind him is open, then once Lois arrives in the scene the door is closed.
Those small bananas are referred to as baby bananas. Plantains are something totally different.
When Joe is going down the hill on his wheelchair he starts moving his legs before he falls and gets up.
When Stewie and Brian are talking in the football game, Brian is drinking alcohol to warm himself up. Stewie tells him alcohol doesn't warm you up since it constricts the blood vessels when in fact it actually dilates them.
When Peter is in the back yard shooting records with the shotgun, it has a pump action on it, but Peter reloads it by breaking down the barrel as if it were a break action shotgun. This makes no sense because pump action shotguns are not reloaded in this manner.