There is another step on the metaphor and simile world.
A step everyone in a culture or group has agreed on. An inside joke so-to-speak.
That is called an idiom.
An idiom is a lot like a metaphor. That’s where it started. My comment about a kitten’s purr sounding like an engine is almost a idiom.
A real idiom may not even have its connection to anything anymore.
Such as ‘Never count your chickens before they hatch’. It used to be extremely common for pretty much everyone to have chickens. Go back to before 1900 and you’ll find chickens with almost every household. Because it gave a quick food option. It was important stable. Everyone understood the meaning too. Even if we had thirteen eggs, that doesn’t mean all of them will turn into chickens. Assuming we’d get the same number of chickens as egg was a fruitless effort. That was the max number, not the most likely.
We still used the idiom.
It’s part of the don’t assume everything will work out perfectly. Because it’s likely you have a bad egg somewhere.
Idioms are cultural. When creating a new world, idioms are something to add to it that will make it more realistic. As a culture grows and exists, idioms will happen. An inside joke for the characters.
How can I add one without making my reader confused? Give your readers some credit. If you use proper context clues, a reader should catch on. And if you really can’t get it clear through context clues add in someone who’s from outside the culture. They won’t get it either. An explanation would be in order. Children and foreigners don’t get idioms without context or explanation. Same as your readers.
Idioms say something about the culture where it’s given. It says something about its myths and religions- current and past. It says something about common activities. It says something about the people living in the culture.
Idioms can turn away people if you don’t know it and you offer nothing for explanation or context. Not everyone gets ‘Never count your chickens before they hatch’. It sounds obviously, but for a new English speaker, it generally doesn’t make any sense.
Watch yourself when adding in idioms. You may be cutting off readers from the addition.
But it can add another depth to the work. I’ll suggest it more than not.