When I was in London for ~3 months for a graduation project for Undergrad, a friend taught me a way to solve a Rubik’s Cube. That toy was perfect for me: I have very willful idle hands, I enjoy puzzles, and I like things one can get better at. It was also perfect for the tube (subway): I had a ~45 minute ride to and from our project workplace every day, this was before smartphones, and reading on the tube made me sick, so something to do was invaluable (talking with my team members was the worst possible scenario, but that’s a different story).
The last 25 minutes of the ride out wasn’t very crowded, so I’d always have a seat, and there’d pretty much always be one or two people sitting directly across from me. I didn’t need to actually look at the cube for the last 5-10 seconds, it was just one of a few different patterns. So I’d watch the people across from me as I finished; they frequently were watching me solve the cube.
They all reacted almost exactly the same way. They’d be staring intently at the cube. I’d finish, rotate it in my hands a bit, and they’d be mildly surprised and very slightly impressed it was finished. Then they’d look up and our gaze would meet, and they’d startle; they always knew/felt that I’d been looking at them while they were watching me finish the cube. That the reaction was so *consistent* was what really stuck with me.
I didn’t fully get what was so interesting about it at the time: humans seem to have a near mind-reading level of prescient knowledge when it comes to eye contact. Was someone looking at me? We’re they staring for a while or just glancing? What were they looking at specifically, and how much attention were they paying?
Its pretty crazy that everyone seems to near-instantly know all of those things without consciously thinking about it. Also, entertaining other people and messing with them a tiny bit when you’re both bored in a subway car is pretty fun.