Fiona Thompson is wearing different shoes once she storms out of the hall. During the fight/dance with her husband she's wearing traditional strapped ballroom-type shoes. Once she starts out down the stairs outside, her shoes are now traditional pumps.
Scott's car has one registration plate, BX03 ZZG, then another, BU03 ZZG, then back to the first in minutes. Later it is revealed that the same car has BX03 ZZG for its front plate, and BU03 ZZG at the rear.
Just past the halfway mark, the killer picks up a red apple, places it back in the bowl, and selects an apple with more yellow coloring, like a honeycrisp. At the end of this episode the apple chosen is a redder one.
When Cully is driving away from Rachel's house and Jacob Stoat is concealed by the side of the road, Jacob is seen eating an apple with a knife. in one shot, the apple is whole, and in the next shot, it has numerous pieces sliced off.
When Barnaby confronts his new Sgt. Scott at Scott's flat, Scott's shirt is nearly buttoned completely. During the conversation, the shirt is nearly open, as Scott begins to button his shirt again.
In the opening panning shot of the open garden festival, a man in the foreground picks up a potted marigold and inhales as though enjoying the fragrance. Marigolds are not propagated for their perfume and in fact smell quite unpleasant.
When playing cribbage with Donald, Mary calls "His Nobs" when she should have called "Nibs" or "His Heels"