Interviewing Tactic
Let candidates know why you're asking particularly complex questions.
Otherwise, they may be distracted by wondering why you're asking. They may stop listening to you and become irritated. They might think you are cross-examining them or may feel anxious if your question seems to demand they provide you with information. You can eliminate these problems if you precede your question with, "Let me ask you a question to make sure I understand what you just said." This keeps you from jumping to the wrong conclusion about what the person has said. It also shows your interest in what your candidates are communicating, which in turn causes them to listen more attentively to you.
Excerpted from Attracting & Rewarding Outstanding Employees