Blond walks in to see her boss. There is a Thermos bottle on his desk. “What’s that?”, she asks.
“That’s a Thermos bottle. It keeeps hot things hot and cold things cold.”
Next day, she has a Thermos bottle too. The boss asks, “What’s in it”.
She proudly says, “Hot tea and a popsicle”
What I’ve never figured out is how a Thermos bottle knows whether to keep the contents warm or cold?