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One fact of history has been misprinted. Ask the historian questions, and when you spot it, call it out.
Ask the historian anything. They live in the changed world and answer as if it were the only one. Questions far from the change get real history.
Read the answers like a detective: anything that doesn't match what you know is a clue. Ask about it!
After every question, the thermometer tells you how close you are: cold cool warm hot. Follow it: ask more about whatever made it warmer.
Stuck? After a few cold questions the historian starts dropping hints.
You win when you call out the misprint: ask about it directly ("Did they dump coffee into Boston Harbor?") or tell the historian what really happened ("No way, it was tea!"). Fewer questions is a better score.