You're sitting next to a stranger who is crying.
Say you see a seat on a train or in a bank with someone on it (it's a three person seat so you'll be one shoulder width apart from them). Only after you sit down you realise the person is crying. Not wailing or anything though.
Do you ask what's wrong/if they're ok or just go about pretending it's not happening?
This happened to me today. It wasnt obvious to me at first because his hands were covering his face and I thought the sniffling was just a cold. I did nothing because I felt it was none of my business.