As is my habit, I began to pass the time with tsumego in the Android app ElyGo. I'm still very much a beginner and do problems whenever I can squeeze them in.
After rapidly completing several problems I ran into one that stumped me. While I stared at my phone intently the elderly Korean gentleman next to me slowly leaned over, extended a single bony finger, and then touched the screen in the proper place to solve the problem.
We did several more problems together, alternating stone placements for those that required more than one move. Then he began gathering his belongings to go.
I looked at him, smiled, and said "baduk?"
He slowly got to his feet, smiled back, said "baduk!", and then shuffled away.
This is the last problem we did together: