Simile is a  comparison between two different things that resemble each other in at least one way. In formal prose the simile is a device both of art and explanation, comparing an unfamiliar thing to some familiar thing (an object, event, process, etc.) known to the reader.

When you compare a noun to a noun, the simile is usually introduced by like:

• I see men, but they look like trees, walking. --Mark 8:24
• After such long exposure to the direct sun, the leaves of the houseplant looked like pieces of overcooked bacon.
• The soul in the body is like a bird in a cage.

When a verb or phrase is compared to a verb or phrase, as is used:

• They remained constantly attentive to their goal, as a sunflower always turns and stays focused on the sun.
• Here is your pencil and paper. I want you to compete as the greatest hero would in the race of his life.

Often the simile--the object or circumstances of imaginative identity (called the vehicle, since it carries or conveys a meaning about the word or thing which is likened to it)-precedes the thing likened to it (the tenor). In such cases, so usually shows the comparison:

• The grass bends with every wind; so does Harvey.
• The seas are quiet when the winds give o're; / So calm are we when passions are no more. --Edmund Waller

But sometimes the so is understood rather than expressed:

• As wax melts before the fire,/ may the wicked perish before God. --Psalm 68:2b

Whenever it is not immediately clear to the reader, the point of similarity between the unlike objects must be specified to avoid confusion and vagueness. Rather than say, then, that "Money is like muck," and "Fortune is like glass," a writer will show clearly how these very different things are like each other:

• And money is like muck, not good except it be spread. --Francis Bacon
• Fortune is like glass--the brighter the glitter, the more easily broken. --Publilius Syrus
• Like a skunk, he suffered from bad publicity for one noticeable flaw, but bore no one any ill will.
• James now felt like an old adding machine: he had been punched and poked so much that he had finally worn out.
• This paper is just like an accountant's report: precise and accurate but absolutely useless.

Many times the point of similarity can be expressed in just a word or two:

• Yes, he is a cute puppy, but when he grows up he will be as big as a house.
• The pitching mound is humped too much like a camel's back.

And occasionally, the simile word can be used as an adjective:

• The argument of this book utilizes pretzel-like logic.
• This gear has a flower-like symmetry to it.

Similes can be negative, too, asserting that two things are unlike in one or more respects:

• My mistress' eyes are nothing like the sun. . . . --Shakespeare
• John certainly does not attack the way a Sherman tank does; but if you encourage him, he is bold enough.

Other ways to create similes include the use of comparison:

• Norman was more anxious to leave the area than Herman Milquetoast after seeing ten abominable snowmen charging his way with hunger in their eyes.
• But this truth is more obvious than the sun--here it is; look at it; its brightness blinds you.

Or the use of another comparative word is possible:

• Microcomputer EPROM (Erasable Programmable Read Only Memory) resembles a chalk board in that it is used for consultation instead of figuring, and shows at each glance the same information unless erased and rewritten.
• His temper reminds me of a volcano; his heart, of a rock; his personality, of sandpaper.
• His speech was smoother than butter. . . .--Psalm 55:21

So a variety of ways exists for invoking the simile. Here are a few of the possibilities:
 

But a simile can sometimes be implied, or as it is often called, submerged. In such cases no comparative word is needed:

• The author of this poem is almost in the position of a man with boxes and boxes of tree ornaments, but with no tree to decorate. The poet has enough imagery handy to decorate anything he can think of, if only he can fix upon a "trim invention." The "sense" he does locate is obscured; the ivy hides the building completely.
• When I think of the English final exam, I think of dungeons and chains and racks and primal screams.
• Leslie has silky hair and the skin of an angel.