John Nolan suffers temporary hearing loss on his left due to a gunshot (clearly indicated in a scene talking to a doctor and Bailey) but later on, there is no sign of this impairment: For example sitting on Bailey's right during a doctor's appointment (exposing his damaged left ear) and not showing any effort to use his "good" side during any dialogue later in the plot.
The "air bubble in the IV" is popular in TV and movies as an untraceable way too kill, but is only deadly in very extreme cases.
When the lady who got attacked in the beginning, goes into the hospital has way more scratches and blood on her face than when she left the house. After she was treated, her face was perfectly clean. No cut, bruises or blood.