Pilot: The Spirit of Christmas (Jesus vs. Santa) - S1-E1
Revealing mistake: Each time Jesus turns his head to speak to the children when he is beating Santa Claus, he has two left arms.
Revealing mistake: Dead lady blinks when Barnaby enters the room.
Revealing mistake: Pretty much throughout the whole show, the iron prison doors do not have any way to lock. Guards put the key in, but there is no actual lock or latch on either side of the door. Even when these doors are pushed shut, there is not a locking sound.
I Guds namn - S3-E8
Revealing mistake: After Beck has arrived at the coroner we see Margareta Oberg's body on a table. Looking closely you can see she's still breathing.