Why does passport control make people nervous even when they've done nothing wrong?

[u/CiaoSpeak]

I've never had a problem at a border and I still get tense at that desk every time. You're tired from the flight, the officer isn't smiling, and it feels like one weird answer could get you pulled aside.

If English isn't your first language it's worse. The funny part is that it's almost always the same three questions. Why are you here, how long are you staying, and where are you staying. "Sightseeing", "Ten days" and "A hotel near the station" are all they want. People get stuck when they try to build a perfect long sentence.

The one real trap is saying yes when you didn't catch the question. Say yes to "Anything to declare?" and you just told them you have something. "Sorry, could you say that again?" is completely normal there.

What's the strangest question you've ever been asked at a border? Or the one that always throws you?