Sarah Monette applies her experience of real-life horses to list five ways in which the actual creature differs from its portrayal in fantasy fiction:
Diana Wynne Jones famously deduced that the horses of Fantasyland are vegetative bicycles. Here are some ways that real horses are anything but:
1. Horses are very large animals. This is something that you can know in the abstract, as we all do, and still be taken aback by when interacting with an actual horse. Horses take up space. Their heads are massive chunks of bone. Even when they're being affectionate, they're still a good eight to ten times larger than a human being, and they are proportionately stronger. [Read on...]
I am not a horse person and will totally cop to a nagging anxiety whenever I write a fantasy scene with riding in it. Sure that I will get called out for reality-defying nonsense, I keep the horses in the background to the maximum extent possible. Fortunately the latest novel is set in a city, with lots of walking and almost no horses testing its verisimilitude.
Another problem, though, is that real horses are disjunctive in most narratives. As Sarah describes, they’re fragile and headstrong animals, both of which traits have a tendency to suddenly disrupt a protagonist’s momentum. (A recent headline reinforces their fragility: the show Luck, in which that fragility was a major theme, has had to cease production after a string of horse deaths.) Well-constructed narratives don’t provide much space for accidents or distractions. If an accident leads to a crucial plot development, it suddenly becomes a contrivance. If it exists only to show that accidents happen, it’s failing the rule of fictional parsimony, which allows only for events that drive the story or in some other way relate to its overall throughline.
Hence the convention of the herbivorous bicycle.