Crew or equipment visible: When Barrett is bringing Susan and Tony their meal, the cameraman's reflection can be briefly seen in the shiny silver lid on the tray.
Errors made by characters (possibly deliberate errors by the filmmakers): When Hugo and Susan arrive at Hugo's house in the Mercedes, with an extended visit in mind, they both go into the house and Hugo leaves the car's lights on.
Continuity: when the two main characters play in the stair, the servant shots a vase with the ball, it falls down and breaks on the floor. The next shot, you can see the bottom of the wrecked vase on the shelf it was on the first place (the rest of the vase is downstairs).