Continuity mistake: Right after Frank gets shot he shoots Portman and you see someone helping Frank get his jacket off as he's lying on the ground. The camera angle changes and you see his jacket back on and someone is starting to help him take it off again.
Continuity mistake: When Frank pursues the killer at the lake house, through the snow-clad forest, his breath doesn't show. But he comes from a warm house directly out into a freezing night air.
Chosen answer: I think he was ticked off because he was being so personally affected by Rachel. He talks about being disciplined. He tries to keep emotions away from his job, but he liked Rachel. Also, Rachel at the time was angry with him, but also showed a lot of disregard for her own safety (as you remember, when he got back it was just after she and Tony went shopping without telling Frank). So yeah, I think it was frustration for the overall situation. To answer your second question, from the conversation with Frank at the lakeside house, Nikki had asked around at a club she went to, but she herself didn't hire Portman. Someone named Armando did the hiring.
Meg Charnley