not sure if this pertains more to call-backs than OCIs, but, i've found that lawyers love to talk about themselves. If it's a different person I interviewed with than in the OCI, i ask them about themselves. why they like working there, what drew them to this firm, what areas do they like to to practice and why, etc. A friend of mine has her PhD in Psych, she tells me to do this. It not only shows that you care about the firm, but also about THEIR personal views, which in term makes them feel good. some crap like that.
If its the same person I interviewed with on OCI, then i pbviously have asked these questions, and normally, i do a search on westlaw for the firm. see which of their cases have been reported, and then read it, and get some questions off it. "i read the X v. Y case, where blah blah, I found it odd the court held that way. what do you think", or some crap. Honestly, these people are looking for a personality fit, you have the credentials, you passed OCI, now they want to know if they can stand to work with you - which is why, i would think, asking questions about their personality, opinion, and feelings, rather than more substantive questions on the law would be more beneficial. (i would think you have already asked about specific areas of the law in ur OCI anyways)
thats my take.