Continuity mistake: During the scene where Gaby and John are in her bedroom talking, she takes a drag from her cigarette while John asks why she isn't happy, but never exhales the smoke from that drag. 23 seconds pass from that drag to the next one and she's in frame the entire time (it cuts between shots of the two of them together and Gaby's close-ups, but doesn't cut away from her). It's also worth noting that Gaby is never seen smoking again at any other point in the series and no explanation is given as to why.
Continuity mistake: When Bree Van De Kamp is sitting on the couch talking to her marriage counselor, as she is doing so she picks up her purse and puts it on her lap, crossing her hands over it. When the camera switches back to her a second later the purse is back on the couch beside her in the exact position it was in before she picked it up.
Continuity mistake: Adam hands Katherine the note he found on the floor written by her aunt in a previous episode. Katherine is holding the paper up. When Adam walks around her in the next shot, the paper is gone and Katherine is only holding her keys/purse. The close up of Katherine (the very next shot) shows her holding the paper again.
Continuity mistake: As the nurse is talking to Susan about the operation, the folding of the paper the nurse is holding on the clipboard changes between shots. First it is half folded over, the next shot it has been folded right over and is being held right down. After this shot it changes again and is now folded back without her moving the paper.
Continuity mistake: When Betty is shown the crime scene photo of Melanie's body, Melanie is inches away from a pallet and the jacket covers most of her torso leaving only the right arm exposed. In the flashback scene, Melanie is feet away from the pallet and the jacket mainly covers her chest and face, leaving both arms uncovered.