Carpe Demon - S7-E14
Revealing mistake: After Leo's meeting on the bridge with two of the Elders, it cuts to Phoebe walking down the stairs as she catches Drake dancing, and when he approaches Phoebe to take her hands, the top of the set with lighting can be seen in the dining room.
Carpe Demon - S7-E14
Revealing mistake: When Miss Donovan is chained up, it is very obvious that her hands can easily slip through the shackles.