In scene four of Lepage and Brassard's Polygraph, the scene seems to offer two important elements to the play: one is a visual representation of François reliving the past—a memory revived; the other is the sense that David is not necessarily the good guy we might assume he is simply because he works for the police.
The stage direction for this scene tells us that David slides over a wall. We might imagine that the wall represents a division François has erected in his mind to attempt to forget the unpleasantness when he found Marie's body and was considered a main suspect in her rape and murder:
David enters the restaurant over the wall, sliding down with his back to it, his arms and his suit jacket spread like a giant, ominous spider. David lands smoothly in the empty seat across the table from Francois.
The fact that David delivers the same questions in this scene as were asked at during the polygraph test allows us to see (with this masterful stylistic element in this live play) that François' memory returns and is haunting him.
A vivid image that cannot be ignored is the author's comparison of David to a "giant, ominous spider." One can imagine that François' mind traps him like a spider's web when old memories surface. We might also infer by the easy manner in which David lands in the chair across from François that this event is something the waiter is not terribly successful at forgetting. David lands smoothly and perfectly, as if he (or the memory) has come so often that it is quite adept at making a seamless entrance into François' conscious mind. It has been six years, but we learn later in the play that the suspicion the police had of François that they have never released him from, still torments him—to the point that he is not sure anymore if he is innocent or guilty. We can also infer it drives him to his suicide.
The fact that David is represented in this old memory as an ugly and dangerous spider gives the audience pause: just because David is a criminologist does not mean he is a decent person. For instance, when he first meets Lucie, she has just witnessed the death of a man who committed suicide by train right before her very eyes. David arrives on the scene, but his very business-like. He shows little emotion over anything, and no concern for Lucie. David shows no surprise or concern when he meets Francois, although he admits in a lecture that the polygraph and the way the police use it often cause long-seated emotional or mental distress. He doesn't even react later in the play when Lucie announces that she slept with François (while David was away) in order to comfort him—this man so tormented by the past. As a giant spider, it is not hard to imagine that David is as methodical and distant as a spider when spinning its victim into its webbing. He offers no comfort and accepts no responsibility. Seemingly an emotionally dysfunctional character, he offers almost nothing in response to any situation he encounters in the play.