Your widespread senses dim.
For a lack of my own catchy phrase for this, let’s call this the “spider sense.” Unless you’re focused on a single subject, you tend to people watch and listen on a wide scale. However, if you’ve found a small event that has caught your interest (say, someone lighting a candle by licking a match first), your spider sense narrows to ponder and consider that single moment (“How did it light? Why lick it first? What trick did they use?”) That means, if someone else is watching you now….you’ll never know.