I know all about quantum mechanics.

Basically, I can't tell if they worked on my car until I open the hood and find a dead cat.

@spaf

Or a living, but very angry, cat.

@spaf where do you go to get the dead cat? That would be at least an interesting story to tell about auto maintenance. All I ever get is “the 12V battery on my Toyota pickup is dead again because I went all the way through the warranty period without starting it”.
@spaf which I guess is actually an interesting story bc I drive an electric car that never needs any maintenance beyond replacing the tires every 30000 miles. The traction battery is apparently immortal.
@spaf
Thank you, I've never heard it explained so clearly before!!!