Faces and people: … Just before 9 o’clock this morning, I saw almost a hundred people practicing tai chi outside of the Lake Merritt BART station, around the 9th Street exit that lets you out on the west side of Oak Street. Their swaying to this thin, high, mercury sound — this flute and voice threnody drifting out of a possessed boombox beside an old man — turned everyone into 4-, 5- and 6-foot-tall trees become human, like forest spirits. (For some reason, I thought of the stalking dance that Michael Jackson and the other zombies do in the video for “Thriller.”) Some wore jeans; others T-shirts and floppy hats. Most were Chinese-American, though I think I saw a white guy or two. I walked right past the lone brother in the crowd, who was concentrated and focused to the point of sweat coating his face and chest in drops. I smiled at him as I passed; I don’t think he saw me.