When someone knocks on your front door when you're not expecting anyone.

[Astreja]

I always associate knocks on the door with a friend calling  even if it is late. There will surely be that one time though when I find two smartly dressed folks at my door asking "what do you think about the state of the world," ?  I think I would do some silly like tell them to hang on a minute. Get them both an apple or some fruit, give it to them, and close the door. That would confuse them.

Smile enigmatically and say "The snake told the truth, you know," just as you're closing the door.