When the hunting party starts, the animals (notably the rabbits) barely move. Even when the beaters are close to them, they move at the last moment. This because the animals were not wild as the plot required, but actually bred in captivity and hence used to human presence. For information, the killing is real: many animals died during the movie.
(around 24 min) When Schumacher and the under-gamekeepers find the cat in the rabbit trap, they complain about it. They release it and the cat runs away to their right. Schumacher immediately turns about 75 degrees to his left and shoots into the far distance (his gun is level). From the characters' dialogue, he obviously "killed it" (!).
(around 23 min.) Two different couples arrive at the chateau at the same time, in two different cars, yet the two license plates are sequential. The white car is 1812RM3, and the black one is 1813RM3.
When you first see Christine and Lisette, there is a man visible in Christine's dressing-table mirror. He moves out of sight a moment later.
After the last characters arrive at the castle when it is raining, Christine and Robert de la Cheyniest say "We will organise a party in a week, after the hunt." However the same evening, Robert says "Let's go to bed, because tomorrow...", implying the hunt will be the following day. And indeed the next sequence is the hunting scene the day after. This because the script was still being modified during the shooting of the movie, hence timelines sometimes varied.
When the party first arrives at the château, a boom shadow falls on the back of the head of the old white haired guy standing there.