I have had an interest in soundtrack music ever since I was a little feller (3-4 years old).
One type of incidental music writing involves what I call "inversion". There may be a music theory term for it, but I do not know it. The method involves taking an extant piece of music and flipping it. One of the most obvious examples is Barry Gray's piece "Formula Five" which was a pop music tune set in far-off 2062 or so on "Fireball XL5". When Gray wrote it, the hot jazz craze of the time included "Take Five" performed by the Dave Brubeck Quartet. It was the record that put jazz on everyone's turntable, and transformed Space-Age Bachelor Pads forever. Here is Brubeck's work, with Barry Gray's inversion below it.
See how it works? I have another one for tomorrow, where a Japanese composer inverts a Barry Gray piece.