An update for my 'informal chat' with POI: turn out it's actually a super informal and casual meeting. My POI let me talk about my study and research - I was nervous so just briefly introduced it. She didn't ask any questions but said there is some research cluster in the department that she thought would interest me and wondered if I have any questions for her. I asked about her current research and she talked about serveral ongoing projects, and briefly mentioned her mentorship style and other students with research interests that overlap with mine. Basically I think I didn't say anything I'm supposed to say as an interviewee/applicant to impress her. Instead, I was totally impressed by her passion and all the interesting projects going on in the department. Now I feel like I would be so disappointed if I couldn't be part of it. My preparation for all the tough and difficult questions is useless, I'm not sure how I should feel about the only interview I got this round...