Last night I was listening to another CD in the Spike Jones box set I bought this past Saturday. There was a tune I heard on the Dr. Demento show, but had forgotten the title. This tune, Black Bottom has no vocal but it does have a joke of sorts in it. The joke depends on knowing one way that a record can fail or be damaged. There is a point where a bit of the music repeats several times fairly quickly, and then there is a *thump* like someone hitting something, and then the tune proceeds. When that was recorded the joke worked because everyone knew what it was.
People of a certain age (I don't know the limit on that) will get joke immediately upon hearing it. I suspect that some people now might never have encountered that problem and might not have picked up on it from cultural references and wonder what that was all about. If that's not the case right now, I expect it will be in not all that long a time.
I've read a few older (well, they're older than I am) books, which I generally find more informative than many recent books. But sometimes an assumption is made that "everyone knows that" which throws me as I, several decades later, have no idea what is really meant since I'm missing that critical "common knowledge."
Another example is a bit in some old movies. One bit that I recall seeing was someone hearing a shot, except it wasn't a shot. It was a light bulb breaking. Today, that doesn't make much sense. Sure, if you broke a bulb it would make a noise. But you wouldn't mistake it for a shot. The technology changed is what happened. For some time now, light bulbs have been filled with gas. With the pressure about the same inside the bulb as outside, if they break, they just break. Those early bulbs weren't gas-filled but held vacuum. When they broke, the atmospheric pressure pressing in caused a sharp implosion. That implosion is as good as an explosion as far as the kind of sound it made.
Those sort of things makes me wonder what I'm missing or not getting because of the "everyone knows that" assumption not working. I also wonder what that is taken for granted now will seem oddly unexplained in the future.