A face loomed in the darkness outside our stopped subway train. Outlined in glowing white lines. Xs for eyes. A hand-drawn, rictus grin. A mask. It bobbed along up and down the cars, pressing against the windows, fingertips tapping the glass. Giggling echoed down the tunnel, accompanying a high-pitched voice asking, “Who smiled? Whooo smiiiiled?”

Within, some of us glanced around at each other, wondering who had broken the taboo. At all stations, ancient signs declared, “Do not smile at strangers.” Relics of a time of scams and con artists. Now the tunnels were too dangerous for casual opportunists. Suggestion had become rule.

The voice of the conductor buzzed over the intercom. “Who pulled the emergency brake? What’s going on?”

In front of me, the face had paused, tilted, as if curious. A bare finger rubbed against the glass. Over and over. “Was it youuuu?”

I swallowed.

Behind me, a woman stuttered a reply to the conductor. “No one,” she explained. “S-someone smiled at a stranger.”

A curse word sounded through the intercom before the conductor remembered to close the channel. Without the presence of an authority figure, the entire car held its collective breath.

The face watched us like fish in a bowl.

As the engine revved, the train lurched forward. Before me, beside the mask, the white outline of a hand bloomed, fingers outspread. They waved cheerfully at me. As the face receded, the voice sang out, “Byeeeeee.”