QUEUING at the supermarket the other day, I was amazed to find the woman ahead of me quite unabashedly looking through my intended purchases as I lined them up on the conveyor belt.

Eyeing up the contents of other people's shopping trolleys isn't a terribly rare phenomenon -- I admit to doing it myself on occasion -- but she then proceeded to enlighten me on what she'd "discovered" about my life in the process.

Like how the packet of cat food meant I owned a pet and other remarkable feats of deduction like: "I can tell you enjoy washing your hair" after examining the shampoo bottle.

As charming as she was about the whole thing, it did feel she was slightly intrusive. At the very least it spurred me to camouflage my sanitary products under a pile of spur-of-the-moment chewing gum.

Now, contrast this episode with one later the very same day. My evening commute was put on hold as the train stopped unexpectedly just after pulling out of the station. Thinking nothing of it, I continued to read my magazine.

There was a yell from somewhere in the next carriage. I kept reading. The police turned up. Still reading.

More yelling, more reading. The conductor asked me if I had first-aid training. I told him I didn't, then turned the page.

This probably sounds heartless -- me skimming the latest fashion column while someone may or may not have been bleeding to death a few seats away.

But seeing that the police were handling the matter and having established there was nothing I could do to help, I didn't consider it any of my business and I would never interfere.

Just like I would never turn to someone buying deodorising insoles and say "I can tell your feet smell like rotting whitebait."

We all possess our own unique sense of the line between healthy inquisitiveness and meddling curiosity, so obviously the boundaries of polite interest waver a bit (or a lot) depending on who you ask.

For me, browsing for a shade of paint to redecorate with involves collecting a handbag's worth of colour samples.

For my husband, it means traipsing through other people's gardens and cupping his hands against their front room windows.

So just where exactly is the middle ground? In other words, how do I go about showing concern for my fellow man without causing him to blush at checkout?