In Ball Lightning, humans are doing experiments with quantum phenomena. They're doing it deep underground in the most isolated environment on the planet. Yet for some unknown reason the wave function keeps collapsing even though there are no observers present.
That's when they realize, there are observers present, just not human. Alien intelligence is spying on their experiment. But shortly after they realize this, the quantum experiments begin functioning as expected, no wave function collapse. The alien observers realize they've exposed themselves, and stop spying on the quantum experiments.
That was pretty mind-blowing, especially after learning about the Sophons in Three Body, which were clearly the alien observers in Ball Lightning.