When Barrett first enters the house, Tony takes his legs down twice before standing up.
When Tony and Barrett play in the stair, Tony hits a vase with the ball and it falls down and breaks on the floor. The next shot shows the bottom of the wrecked vase on the shelf where it had been in the first place (the rest of the vase is on the stairs).
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.
When Tony and Susan arrive at Tony's house in the Mercedes, with an extended visit in mind, they both go into the house and Tony leaves the car's lights on.