When Donald unlocks the apartment door, we hear several deadbolts being undone, but when the door opens there is only one deadbolt striker plate on the door frame.
When Walter goes in the tank, Olivia says his heart rate is "a little low", when his heart rate is 62 beats per minute. 62 is actually a normal "resting rate", meaning the heart rate of someone lying relaxed, flat on his back, not engaged in any physical or mental activity.