Feel free to ask :
- question to interviewer about his carreer and experience at the firm > take good notes at the begining of the case when he's introducing himself
- question specific to the office current business
- question regarding your future integration process
- bullsh** general questions on the firm that could be answered from reading the website
- question that could communicate a negative mindset : asking about the working hours (you should know what to expect at this stage), asking about the salary (this will be revealed once you get the offer, if you want to know it in advance try to reach consultant offline not during interview), ..