If the jury returns a verdict against your client, it always makes sense to request that the jury be polled. But what does it mean to "poll the jury"?
After the jury has returned its verdict, but before it has been retired, any party has an absolute right to request that the jury be polled. Upon this request, the judge or court clerk asks each juror individually if he or she agrees with the verdict. The judge has discretion about how to word the question, but the usual form is to ask: "Was this then and is this now your verdict?"
If a juror does not affirm the verdict by answering yes, you should ask the judge to ask follow-up questions. You should also make a record if any of the jurors hesitate in answering the question, e.g., "Your Honor, if I may? I would like the record to reflect that Juror #2 hesitated for ten seconds before answering, which indicated some reluctance on her part to affirm the verdict. I request that your Honor question Juror #2 about the reason for her hesitation."
Failure to make a complete record waives the issue on appeal. If any juror disavows the verdict, the judge can either discharge the jury or instruct it to return to its deliberations; in most cases, the judge will do the latter. See, e.g., People v. Smith, 649 N.E.2d 71 (2d Dist. 1995).
This short summary of the polling process is drawn from numerous cases. A typical case that explains the process is People v. Gunn, 604 N.E.2d 1044 (3d Dist. 1992).