When Derek rides Avatar for the first time, the horse has no reins or bridle. When he returns, it has both.
LeBorg tells Lady Jocelyn that the wine and oysters aided his recovery, but we've seen nothing of wine and oysters. Clearly a scene was cut, as this line makes no sense in this context.
Throughout the film, a character's voice will suddenly change, even in mid-dialog. (Probably the work of voice specialist Paul Frees.)
A hay rake was put next to the rock wall by the killer after dragging the fox in the bag around the hunting area. In a later shot near the end of the fox hunt, the hay rake is pulled away by a tractor for a clearer shot of the field of hunters. After the dog sniffs out the killer, the killer jumps a horse over the wall and gets killed on the hay rake as he falls from the horse.
When the Rev Mr Atley says he hopes he is not overweight, the attendant says he is over by three pounds but the shot of the scale shows the weight is in kilograms.
The closer shots during the fox-hunting scenes were shot in a studio using rear projection. In these shots, wires can be seen holding the actors and allowing them to move up and down as though riding real horses.
Gwendolynne La Doll's address is shown on the manuscript as being on Fulham Road, London S.W.8. Later dialogue describing the location as "the Fulham Road" makes it clear that the main street has that name. But this runs from Fulham to Brompton, whereas the SW8 postal district lies across the Thames in districts such as Battersea and Wandsworth.
At 0:50:19, Mrs Karoudjian refers to her husband as "Mr. Kadjourian".