Revealing mistake: In the scene were Mrs Doyle is listing the rude words and phrases used in one of Father Ted's favorite author's book's, she goes through all of them fine. Apart from the last one, when she says "Get your boll*cks out of my face" you can hear her laughing in the word "boll*cks" before she exits the room.
Continuity mistake: As Father Crilly is shouting at Father Jack "No, not your room, not your room." to get up out of the spare bed, watch closely and as Father Ted strikes him in the face, notice that his hand doesn't even touch his face, and his hand stops several inches away from his face, using only his reaction and the sound of a punch to illustrate a punch at all. (00:18:15)