As Mark pours champagne for him and April, when he raises his glass to toast (April's POV), his drink has a layer of froth on top, in the next shot (his POV) all the froth and bubbles have instantly disappeared and both their drinks are completely still.
When Mark and Jez are riding the national express bus they are discussing Dartmouth University. When Mark asks Jez if he ever appealed his degree David Mitchell mistakenly says "Did you ever appeal your degree, Mark?' to Jeremy.