At my latest interview, I got asked about an example of a situation where I was in a group and two of us disagreed on something, and only one of us was right. I had no idea what to say, so I said "Well, to be honest, I'm drawing a blank on a specific example, but I can tell that in that situation I would do x, y, and z." The interviewer smiled and said "Oh, that's ok, it's not a common situation."
Accepted soon thereafter. Being able to admit you don't know something is crucial in medicine; you can't let your pride get in the way of good patient care. That starts with your interview!