Wait for a good answer and avoid talking too much Waiting in silence can be awkward for both you and the candidate. Social environments usually encourage us to fill in silences with conversation. Resist the temptation, since you will distract the individual's concentration, and you may even inadvertently prompt the candidate with clues to the answer you want to hear rather than their own answer. Once you have posed a question, allow the candidate time to think about the response, even if they seem to struggle a bit trying to think of something. Once you break the silence or move to another question, you have excused the candidate from demonstrating that they have the skills you need in your position.
Some candidates are natural talkers, and can fill silences without actually answering the question.
Ask the hard questions Just because a question may be difficult or uncomfortable to answer doesn't make it inappropriate or discriminatory to ask. Supervisors are sometimes reluctant to ask candidates why they left previous positions. It's okay to ask them about specific aspects of previous positions that they found to be difficult. If those same factors exist in your position, the candidate may not be a good match. Sometimes, however, the circumstances that caused problems for them in the past are not present in your position or were personal and have been resolved.