Changing out a wall switch, I have my sister helping me. She tells me when I found the right breaker and I go up to change the switch. I tell her "just because you've turned off power doesn't mean the box is dead." I check the second switch with a non-contact voltage detector (aka Death Stick) and see no light. But I turn on the second switch anyway and the ceiling fan turns on!
Good teaching moments sometimes just show up.
Puckdropper