When Thomas has his meeting with Miss Baxter, he locks them both in. The key makes a characteristic noise in the lock. However, when Miss Baxter opens the door to leave, she does not turn the key and there is no characteristic noise. She's just opened a locked door.
Near the end of the episode when the family is gathered in the library, behind them Carson enters the room twice.
Throughout the horse race Mary is seen riding sidesaddle, but as she jumps the hedge it's clear for about 2 seconds that she's riding astride.
The maid Denker is, in the closed captions, listed as Denka.
During the first horse race, as they round the track in the final lap, you can clearly see a cell phone tower in the far distance.