In the opening and ending scenes where Caroline enters the bathroom, a note on the wall can be seen, which says "DO NOT TURN ON". That's a note to the cast and crew not to turn on the ceiling light in the bathroom otherwise it will trigger the exhaust fan which will generate very loud noise.
In the pub scene, a girl was seen vomiting on the steps. As the camera change back to the lead characters, we can see the same girl sitting by the table back to the camera.