Honey: I didn't know until just a minute ago that you had a son. George (Wheeling as if struck from behind) WHAT? (1.388-1.389)
Martha has committed a cardinal sin by mentioning her and George's imaginary son to other person. It's this action that eventually causes George to destroy the illusion of the child forever.
George: the one thing in this whole sinking world that I am sure of is my […] chromosomological partnership in the…creation of our…blond-eyed, blue-haired…son. (1.649)
It's pretty ironic that the one thing George believes is not an allusion is the creation of his son. Of course, we learn by the end of the play that their son is completely fabricated.
George: national boundaries, the level of the ocean, political allegiances, practical morality…none of these would I stake my stick on anymore (1.649)
This statement points out that even things that seem so finite to masses of people are really just agreed upon illusions.
Nick: I married her because she was pregnant. […] It was a hysterical pregnancy. She blew up, and then she went down. (1.49-1.51)
It's interesting that Nick and Honey also had an imaginary child. There is, however, a major difference between the two: Honey and Nick's imaginary child, unlike George and Martha's, was never "born."
Martha: Georgie boy had lots of big ambitions. In spite of something funny in his past. […] Which Georgie boy here turned into […] A novel all about a naught boy child […] who killed his mother and father dead. […] George: STOP IT, MARTHA! (2.448-2.462)
We wonder what part of George's novel was true and what part was illusion?
George: Martha didn't tell us all about by my second novel. […] this nice young couple comes out of the Middle West, and he's blond and about thirty […] his mouse is a wifey little type who gargles brandy all time (2.520-2.522)
It's interesting that George exposes the truth of Nick and Honey's relationship, by imagining a fictional work of fiction. In a way he's using the illusion of an illusion to strip away all illusion.
Martha: Can I get you a drink, Martha? Why, thank you, George; that's very kind of you. No, Martha, no; why I'd do anything for you. (3.1)
Here we see Martha alone and pretending to have a nice civil conversation with George. It's interesting that this is the game that she chooses to play when by herself.
Martha: Truth and illusion, George; you don't know the difference. George: No, but we must carry on as though we did. Martha: Amen. (3.161-3.163)
Martha and George seem to agree that there's no such thing as an objective reality. Once you pull one illusion back, you'll only find another.
George: We got a telegram; there was a car accident, and he's dead. POUF! […] Martha (A howl which weakens into a moan) NOOOOOOoooooo. (3.449-3.450)
With this, George destroys the illusion of their child. Are they better off or not?
George: Who's afraid of Virginia Woolf, Virginia Woolf, Virginia Woolf,[…] Martha: I...am...George...I...am...(3.541-3.544)
Many say that the title of the play is code for, who's afraid of living without illusion. With the last line Martha admits that, like many, she's absolutely terrified.