I did interviews for geography and got an offer this year. I was nervous about the interviews, but they were actually not that bad. In fact, they were quite an enjoyable experience once I got over the initial nerves. Hopefully, if you really like what you're studying, you'll find being asked such challenging questions and having the chance to respond to them actually pretty fun.
The interviewers are really helpful and don't want to give you a hard time. You'll feel nervous, but don't let it put you off because they're not trying to catch you out or anything - they just want to see how you think and how you'll respond to challenging and interesting questions. Don't worry about feeling like an idiot - the questions are meant to be hard, and they will need a bit of thinking time. The main thing is not to rush your answers.
Now, they might purposefully ask a bit of a screwball question - I had one interviewer who specialised in gender studies ask me some crazy question that threw me off a bit - but again, it's not to catch you out and gives you an opportunity to show you can think outside the box a bit, so again, just don't panic and rush your answer.
Some useful advice I got was also to challenge source material they give you - sometimes source material you get isn't really enough to adequately answer the question you've been given - eg it might make assumptions or tell you about only one aspect of the question - so don't be afraid to point that out because those are exactly the sort of skills they're looking for.
Hope that helps and your application goes well, good luck.