Continuity mistake: As Lydia cleans off the coffee table and walks out with the tray the green pillow on the left of the couch is at the center of the screen. No one touches it but a few shots later as Melanie brings Cathy back from the bathroom it's been fluffed up with the right corner now being higher than the left.
Continuity mistake: When we see Melanie sitting with Cathy on the couch, as Mitch checks the windows, the coffee table with the coffee pot on it is between them and the ash tray on the table to the left of the brown chair. Later when Cathy asks, "Mitch, can I bring the lovebirds in here?" we see the ash tray and plenty of space to the right of Cathy but the coffee pot has been moved out of the way for this shot.