There was not one specific difficult question asked, but I will say they are very interested in understanding why you chose a specific solution for a project. They asked many questions that delved into my thought process - i.e. how do your ceiling forms relate to your original concept? I would liken it to a more relaxed and friendly critique than l experienced during my college years - just be prepared to defend your design in a way that relates to the job you're interviewing for.
