When Mary suggests David has a day off, he is wearing a green shirt (no cardigan). In the same scene from a different angle, he has a cardigan on.
When Mary falls down the stairs in her underwear, an apparent stunt double clearly has bare feet, but in the very next shot Mary has sandals or slippers on her feet.
When Mary enters her room and sees that Lucinda has vandalized it, we see that Lucinda wrote her name on the door, as well as Mary's name crossed out. There's also a blue towel or piece of clothing hanging on the door. But later in the scene, these words and the towel are gone, replaced by the word "whore" and another word lower down.