Mindless and irresistible as chain letters or online surveys, most internet challenges are like Michael Corleone’s mob in “The Godfather: Part III.” You imagine you’ve given them the slip and they suck you back in. As a rule, I avoid these seductive time traps. Yet there I was recently, scrolling through Instagram for the 10th time that day, when I stumbled on the Seven Day Book Cover Challenge and was instantly hooked.

Actually, that’s a misstatement. This innocuous game, which asks users to post a photo of a book cover on a social media platform every day for a week, requires an invitation; it is a challenge, after all. Since no one had actually tagged me, I figured I’d ask.

The person I approached was the fashion illustrator and stylist Bill Mullen, whose droll feed — equal parts memoir, style commentary and grim account of a renovation from hell conducted by an upstairs neighbor he refers to as Minnie Castavet — has become digital catnip for those of us hooked on a growing trend for using Instagram to write long.

Some Literary Show-and-Tell

Mullen himself had been challenged by @thebookmarc, the bookselling branch of the designer Marc Jacobs’s empire, and his daily book posts skewed irresistibly toward oddball obscurities.