Then something curious happened: It mutated. Since everyone who participates is supposed to paste the original instructions into her own note, it’s easy to tinker with the rules. Soon enough, 16 things (and 16 tagged friends) morphed into 15—and 17 and 22 and 35 and even 100. As the structure crumbled, more users toyed with the boundaries. Like any disease, “Random Things” was mutating in hopes of finding a strain that uniquely suited its host. In this case, the right number was vital to its survival: The more people who are tagged, the more likely the note is to spread. The longer the list, though, the more daunting it is to compose and the fewer participants will be roped in.