Not sure if it counts as an illusion but one that comes to mind is Gorillaz - Clint Eastwood. There's a line "remember that it's all in your head" that was mixed in a way that phase cancellation will make it inaudible on mono playback.
> was mixed in a way that phase cancellation will make it inaudible on mono playback.
That’s just what happens to the surround channel in audio tracks produced using Dolby Stereo, when, as you say, they are naively mixed to mono. This happens all the time.
https://www.youtube.com/watch?v=1V_xRb0x9aw&t=176s Now go and install: https://addons.mozilla.org/en-GB/firefox/addon/soundfixer/ and set output to mono and replay it.