Take, for example, a domestic drama about a couple falling apart. They fight, they break up. They go their separate ways. One of them falls ill and dies. The other goes to the wake, to remember their good times. At the wake the body stands up and starts eating brains. Now it’s a zombie story.

You could build the possibility of zombies into the rules of the story, the way “A Good Man Is Hard to Find” starts with the grandmother not wanting to go to Florida where the criminal called the Misfit has broken out of prison, and ends with the Misfit killing the grandmother—you could make the illness mysterious or give one of the lovers a dream about zombies or set their first date at a zombie flick—but it’s not necessary that you should plant these kinds of seeds.

It’s not actually prior rules that make zombies seem like a frustrating turn of events or an interesting one. Some of it is personal taste or the question of audience—I never questioned the bike ride in my MFA workshop because I didn’t care whether a bike ride could go on all day or not; I would be happy to see zombies interrupt a familiar domestic story. On a craft level, the complaint that something is not “believable” or “realistic” or that we don’t “buy it” or that it’s not “earned” is really an indication that the story doesn’t seem to recognize that something unusual has happened. This is why planting seeds is one way to make the change read more “smoothly.” But it’s not the only way.