What is the difference between a voir dire and an appellate court?

"The appellate court, on the other hand, must judge the existence of a prima facie case from a cold record. An appellate court can read a transcript of the voir dire, but it is not privy to the unspoken atmosphere of the trial courtthe nuance, demeanor, body language, expression and gestures of the various players. [Citation.] ... [T]he prima facie inquiry is so fact-intensive and so dependent on first-hand observations made in open court that the trial court is better positioned to decide the issue...." (Tolbert v. Page, supra, 182 F.3d at pp. 683-684.)