Assume that you've done all the prior preparation you can possibly do. You've studied the Interviewing Series, you've practiced, you've tried to guess all possible questions that might be asked of you.
And, yet, when the interviewer asks Question X, you're caught off guard for whatever reason. Maybe you were thinking about your previous answer. Maybe you were unusually tired. Maybe it's just nerves and you forgot even a well-rehearsed answer. In other words? You're blanking.
What phrases can be kept in one's back pocket to gracefully mitigate this occurrence? If it's a technical question that you objectively don't know the answer to, I understand that it's easy to flatly say, "You know, I'm not 100% sure about that - but I bet I could find out quickly...etc". But what about a conceptual / qualitative question?
In other words, what's better than "I don't know.", "I can't remember at the moment, actually." or "Can I get back to you on that? For whatever reason, I'm drawing a blank."