Knowledge: Sisters tend to cross each other's borders to make each other upset while, USA and Canada have sister relationships but require passports at all times to enter and exit.

Conversation:
My moms family lives in upstate New York, when I was a kid I got to walk over to the Canadian side and had the most beautiful view of Niagara Falls. Only went once but I remember it like it was yesterday. Do you know anything about it or have you seen it?
I know that it is the collective name for three waterfalls that straddle the international border between Canada and the United States.
Oh, I see. I want to go back and see Niagara Falls again. Do you think I can cross the Canada and the United States border without a passport? I heard they are sisters.

Response: Of course yes. Even though they have a sister relationship, a passport is required to enter and exit the USA and Canada.