Continuity mistake: Danny and Jamie are at the pistol range shooting targets. The vantage point from down range shows them both shooting tight shot groups. However, when they are finished shooting, they hold up their targets; their shot groups are not as tight as the down range perspective. (00:34:01)
Continuity mistake: Danny and the ESU enter the warehouse basement to find Bobby, and when they start to return fire, the first guy they shoot knocks over the white plastic lawn chair (beside the recliner) as he goes down. Then, in the next shot facing the door, that white lawn chair is upright (not the yellow table chairs), but in the next shot it's lying on the floor again. (00:32:40)
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.