(SPOILER) Why did they invent him?
For what purpose did George and Martha invent an imaginary son? Since it was supposed to be his 16th birthday, had they started the delusion 16 years ago?
For what reason...to save the marriage? I find that hard to swallow...they fight about their son. The color of his eyes, the birth itself, their different parenting styles. The son only served to bring out more hatred, frustration and anger between George and Martha, and so again, I have to ask: WHAT WAS THE REASON FOR HIM?
I have a friend who owns the DVD and he maintains that Martha HAD a son, but for some reason she had an illegal abortion (maybe because it wasn't George's...Martha brings that very subject up in front of Nick and Honey.) Then she finds out she can't conceive with George and the guilt from destroying what will be her only pregnancy drives her mad with guilt and self-hatred.
George somehow finds out about it, and tortures her emotionally over it. The imaginary son is a way to hurt Martha---to continually remind her of her infidelity.
Just a thought...