Dr. Cox will just be trying to rattle you to see if you:
a: can handle a bit of high pressure and
b: will stay within your ethics and principals under said stress
He is actually a very effective and articulate professor. His function in the interview is to try to get you to set off his bs meter or lose your composure. The likelihood is that if you draw Dr Cox as an interviewer, it's because this is the part of your application they're most concerned about. Above all, don't be afraid of Dr Cox, or any other interviewer for that matter. Be professional and polite, but firm and confident in your principles. The best response to an ethical question, or any question for that matter is one that is sincere and well reasoned, and NOT the answer you think the interviewer might want to hear. If you can stay within this with Dr Cox intently staring at you
, he will respect you and you will probably get a positive result. If you begin to contradict yourself, Dr Cox will smell blood in the water and you will be eaten alive.