Dannie's quote of the day

I suppose this subject is one that every parent in the world dreads, Talking to strangers.
I can honestly say this is one of the hardest things I have had to try and explain to Dannie.
A perfect example is when Dannie first started speaking to anyone and everyone, actually she still does. But in this particular incident we were on a bus home and I was starting to tell Dannie how dangerous speaking to strangers would be, I told her what every parent does that they may take you away and that I may never see her again which to me was a frightening enough way to make it very clear that some strangers are dangerous.
Dannie's answer was " what is a stranger" and I replied that it was someone you didn't know. Dannie being Dannie asked "how do I know if I know them" the conversation was getting intense and if I'm honest rather confusing so made it as simple as I could and told her. "if you don't know their name then they are a stranger" simple enough to understand I hear you say, well, this is Dannie so she did no more than to turn round to a lady sitting behind us on the bus and proceeded to ask the lady"what is your name" The lady was quite taken aback by the sudden conversation so the lady asked Dannie "why would you need to know such a thing" and Dannies answer as I'm sure you have all worked out by now was " well if I know your name then your not a stranger anymore.
How do you answer that?