Mind Games - S9-E3
Continuity mistake: At the dinner table, after Edie plays her prank, the camera is opposite her. It's behind Danny and his sons. She sits down and puts asparagus on her plate. Two seconds later, the camera is now behind Pop. She picks up asparagus to put it on her plate, which is empty.
Milestones - S9-E12
Continuity mistake: Jamie is arresting a subject after he drops a knife. Jamie kicks the knife away from the subject and it lands next to the brown box and under the red wording on the box. In the next frame, the knife is now just behind Jamie's right knee. (00:05:10)
Answer: It's a common cop show plot device. If the police on the show always acted in the most logical way (i.e. not alerting a suspect to their presence) the show wouldn't have the opportunity for an exciting foot chase.