After Peter takes a bite of his mutton joint (after waving it across his face, as Maid Madelaine did with her fan) she comes up to him and asks "would'st though take a gander underneath my frock". While she is saying this, the mutton joint is back in the basket, unbitten. After the Black Knight arrives to lecture Peter, the mutton joint has a bite out of it again.
When the kids are singing their goodnight song Stewie climbs up and rests his head on the landing, but in the next shot his head is resting on the 2nd step down from the landing.
After Lois gives Peter his lunch when dropping him off at the renaissance festival, the passenger seat door opens up in the wrong direction.
The car door opens backwards when Peter steps out of the passenger side to enter the fair. This is mentioned on the commentary for this episode.
When Lois is dropping Peter off at the festival, Peter opens the door. Instead of swinging forward it swings towards the back of the car.