Drawing up a shortlist means cutting through the pile of applicants until you have a selection of candidates that you would like to request for interview. Unfortunately people often apply for jobs that they are obviously under-qualified for.
Interviewers often have a number of set questions which they ask every candidate. These questions are based around the requirement of the job, and by asking the same questions, they can draw a direct comparison between each candidate.
Normally the interviewer shouldn't be tempted to talk too much to fill any potentially uncomfortable moments of silence. The silence can from the interviewers point of view be a very effective way of encouraging the candidate to offer up more information.
Interviewers must remember that what appears to be a more informal chat than a 'grilling' tends to put a candidate at ease to get a more honest response. This gives valuable insight into the candidate's personality traits, rather than simply an understanding of their skills and experience.