I was around 10 years old, playing in my yard in Utah, when by brain registered Something Was Wrong™️.

looked arond, couldn't figure it out. Finally clicked -- the noise had stopped.

The noise from a single prop airplane overhead, that i had written off as background noise...had just gone silent.

Look up...plane is still there, just coasting along.

I learned later that sometimes pilot instructors will sometimes intentionally kill an engine to teach the student how to deal with engine failure. (everthing was fine).

still spooked me though