You're home with a grown-up busy upstairs when there's a knock. You answer it. A friendly adult you don't know is standing there. They say they're a delivery driver, or doing a survey, or looking for a neighbour — and they ask a question that needs an answer: is your mum or dad home? Are you here on your own? They seem perfectly nice. Nothing about them is obviously wrong. But something in the question — are you on your own? — makes a small flag go up somewhere in your mind, even though you can't say exactly why. You don't want to be rude to a friendly person. But you're also not sure how much a stranger at the door needs to know about who is and isn't home.