Re: Invasion of the Body Snatchers (1956)
So now, having listened to the commentary and watched your little video, I can say that I still don't get what the joke was, but Trey has never looked better.
But seriously folks, the original story goes into a lot more detail about how and why the pods work. Part of the impact of the film may have been that unnerving sense that we don't even know all the rules of the situation, but the filmmakers would have had a back story to work from that they just left out. Modern movies still do this (WTF is a Balrog to those who haven't read LOTR?), but there's a better sense of what people need to know in order to pass fridge logic.
The story also has a much clearer allegory going on, so even if the filmmakers weren't aware of it, enough of the story came through on screen that the audience got it, and this film was supposedly one of the big influences on Night of the Living Dead a decade later.