A common trope, particularly in horror or thriller stories, is the throwaway character. The blonde in the tank top who wanders in the monster's jaws, the jock who jeers at the mysterious MacGuffin and promptly snuffs it. It's an excellent and easy way to show the reader that this situation is dangerous, people can and will die, and we need to take these things seriously and not push random big red buttons because they're shiny, but without having to throw anyone we really care about under the bus.

I'm not talking about the big sacrificial scenes at the end of the book, either. Not deaths that mean something - only deaths that are purely there to show the reader that this story means business. To show you that when you are infected by an alien, you die, horribly, and it's something that the characters are justified in being scared of.

But you can't just throw the lambs in wherever, or because you can't think of an easier way. There are some particular ways and means of using them that are essentially verboten, because the damage they cause to the reader's experience of the book is irreparable, especially if the character concerned hits more than one category.

There aren't many things you can do that'll have me instantly piffing your book to the other side of the room. Sure, if your book violates multiple 'Good Writing' rules, like introducing twelve narrators in the first hundred pages, having an ancient species evolve under a blue hypergiant that still exists, and failing to grasp the basic process of stellar formation, I'll plonk your book down unfinished in my 'don't bother' pile, and pick up the next.

The 'next' will not likely be a book by you. You're in literary-Azkaban, unless you've previously proven yourself of good standing.

But I do like to give a book a chance. A clumsy line here and there, a plot hole, a character whose motive's a little contrived, or some worldbuilding that went a bit askew with the laws of physics - I can forgive these. We're all friends here. But I do have pet hates. And of them, the unimaginable monster is one of the worst.