@malwaretech reminds me of a short video that was shared with me:
Electrician (holding camera): "Who did you say wired your house again?"
Customer (in another room) "My cousin"
Electrician: "Okay, and when did his house burn down?"
Customer: "Oh, about two years ago... Wait, how did you know his house burned down?"
(As this happens, the electrician is showing that there's 120 volts between the customer's oven and metal countertop, capable of supplying enough current to light a lightbulb.)