Metaphor as Definition
An often overlooked use of metaphor is deepen the definition. This is especially effective when the actual definition is a word that may be unfamiliar to some readers. A good example is this one which immediately follows a character using the world carnivorous:
“Yes, meat is a staple.”
The Allusive Simile
A very popular use for similes is to make a comparison between a character in the story and a more mythic figure. This allows for a greater universality of understanding, although in this case those lacking a familiarity with some of the more famous tales from the Bible may be utterly lost:
“You could see why at first they looked at him like a kind of Jonah, or worse a kind of Judas even.”
The Weird Comparison
Sometimes a reader comes across metaphorical imagery that seems just kind of weird. Or offbeat. Or unusual. Maybe it makes sense and maybe it’s just the author allowing a character to be playful. This can be an effective use of simile, however:
“I'm as full of forebodings as a stupid old man, I must dream.”
Purpose
It is not exactly the most common use of metaphor, but when used it can be especially useful: metaphorical language to convey the purpose of characters upon the plot:
“That was your choice on New Tahiti. Water and sunlight, or darkness and leaves. But men were here now to end the darkness, and turn the tree-jumble into clean sawn planks, more prized on Earth than gold.”
"A rat can be a pet, but not a friend.''
Good advice to those studying human beings. Or maybe it is bad advice. The point being that no matter what kind of animal life is being used for scientific study, one must remain emotionally detached. Of course, this is metaphorical advice that is only used among those conducting the study, not those being studied.
