When someone chimes in a conversation from another room, it's almost automatically funny.

This is one of my college friend's ironclad laws of humor.

Why does it work?

Humor requires a prediction error: for something unexpected.

When someone is within earshot but not visible, we forget they're there… but later they can pop back up in the conversation.

We forgot they'd have thoughts on the proceedings because we weren't thinking about them, but they still cared.