Marcella is eighteen and lives in a Texas suburb so quiet that it sometimes seems like a ghost town. She downloaded TikTok last fall, after seeing TikTok videos that had been posted on YouTube and Instagram. They were strange and hilarious and reminded her of Vine, the discontinued platform that teen-agers once used for uploading anarchic six-second videos that played on a loop. She opened TikTok, and it began showing her an endless scroll of videos, most of them fifteen seconds or less. She watched the ones she liked a few times before moving on, and double-tapped her favorites, to “like” them. TikTok was learning what she wanted. It showed her more absurd comic sketches and supercuts of people painting murals, and fewer videos in which girls made fun of other girls for their looks. When you watch a video on TikTok, you can tap a button on the screen to respond with your own video, scored to the same soundtrack. Another tap calls up a suite of editing tools, including a timer that makes it easy to film yourself. Videos become memes that you can imitate, or riff on, rapidly multiplying much the way the Ice Bucket Challenge proliferated on Facebook five years ago. Read more at The New Yorker.