When riding in Nick's car for the first time, Tracy asks him about his allergy to sunlight. She says she believes it's called "phototropic or something?". Nick acquiesces. Phototropism is actually the process by which plants turn towards the sunlight. The correct word she was looking for is "photophobic".
When Tracy finds Vachon at the morgue, his right hand is missing. When she regains consciousness in her car with him driving with both his hands, she simply says "your hand" and doesn't question it further.
Vachon tries to hypnotize Tracy, who has her gun pointed at him while he drives her car, to convince her to let him take a shower at her place and take him to the "Salvation Army for some clothes". She resists his mesmerism. He offers "what if I can tell you something about the crash?" So this is the motivation for Tracy, a police officer, to allow this stranger to take a shower at her place. This makes even less sense when after his shower Tracy says "you were gonna tell me something about the crash" and Vachon replies "no time, I have to go!"