When Nina's water breaks, Mabel's arms go from being in front of her to up by her face in between shots.
The secret tunnels have large holes in the walls with light coming through them. This means that there would be large gaps in the walls of people's apartments, letting them see into the tunnels.
When a tight shot shows Charles' record spinning, three songs are listed on the label, despite a visual groove separation indicating at least five songs on that side of the album.