In Who's Afraid of Virginia Woolf? characters yell all kinds of incantations, curses, exclamations, and prayers. There's "Snap!," "Poof!," "Nuts!," "Jesus!," "Amen" and "Ha!" All these are part of the absurdist comedy, a satire of our American values and religious services. Albee turns the modern family into drunken, spiteful pagan worshippers during an exorcism in which they're all possessed by demons.
First, George uses the gun as a red-herring (misleading symbol of violence). Instead of literally shooting Martha, however, George barrages her with words, insults, dares, jibes, puns, and sarcasm throughout the pay. George has a sadistic and ironical sense of humor, and words are used as weapons. They are more damaging than real bullets from the gun.
Also, the gun is a phallic symbol of manhood, which Martha says George is lacking in. Instead of bullets, the gun shoots a harmless umbrella. So, its symbolic of George's infertility or lack of machismo.
George is the first to say, "Poof." He says it to Nick when Martha and Honey are off-stage:
She was a good witch, and she married the white mouse with the tiny red eyes and he must have nibbled her warts or something like that, because she went up in a puff of smoke almost immediately. Poof!
Immediately, Nick echoes him: "Poof!" And George re-echoes: "Poof!" Later, George will say "poof" to Martha when he kills their imaginary son. Honey, through all of this, can barely follow the conversations, let alone the insults, and so she echoes "poof" too, just to play along.
"Poof," as you know is an incantation one says when something or someone disappears. It is used to express the theme of "reality vs. illusion" in the play. George refers to Martha as a good witch who went "poof" and become a bad witch. Honey's pregnancy is the same: her belly puffs up and then goes "poof" and her child is no more. George's son existed, and the he says "poof," and he is dead. So, part of the absurdist comedy is trying to figure about what is truth and what is a lie, who is good and who is evil, and what is real and what is false. In short, a death (of a child or a relationship) can make one's dreams disappear instantaneously.
Not only do the characters utter epithets incessantly, but they have weird habits: Martha chews ice, Nick mispronounces words, and Honey peels labels. I've always known the act of peeling labels to be a sign of sexual frustration. As Honey is sick all the time and does not have kids, this would apply to her marriage with Nick.
A label is an outer layer, or mask, for the bottle. It hides the contents of what's inside. As George says in Act III:
We all peel labels, sweetie; and when you get through the skin, all three layers, through the muscle, slosh inside the organs--them which is still sloshable--and get down to the bone...there's something inside the bone...the marrow...and that's what you gotta get at.
Then, George mentions the son. So, the son is the marrow is the label. The two children that these two couples don't have are the sources of their dysfunction. These children stand for the broken dreams, the fears, the lack of communication, the baggage, and the names called and masks worn by each couple in their marriage. These lables are real and imaginary, and they can be used as hurtful words or healing wounds. So, Honey's peeling of labels is her attempt to diagnose her own problems (sickness, infertility) and her marriage problems with Nick.