A metaphor is a poetic device that deals with comparison. It compares similar qualities of two dissimilar objects. With a simple metaphor, one object becomes the other: Love is a rose.Although this does not sound like a particularly rich image, a metaphor can communicate so much about a particular image that poets use them more than any other type of figurative language. The reason for this is that poets compose their poetry to express what they are experiencing emotionally at that moment. Consequently, what the poet imagines love to be may or may not be our perception of love. Therefore, the poet's job is to enable us to experience it, to feel it the same way as the poet does. Let's analyze this remarkably unsophisticated metaphor concerning love and the rose to see what it offers. Because the poet uses a comparison with a rose, first we must examine the characteristics of that flower. A rose is spectacular in its beauty, its petals (花瓣) are nicely soft,and its smell is pleasing. It's possible to say that a rose is actually a feast to the senses of sight,touch, and smell. The rose's appearance seems to border on perfection, each petal seemingly symmetrical in form. Isn't this the way one's love should be? A loved one should be a delight to one's senses and seem perfect. However, there is another dimension added to the comparison by using a rose. Roses have thorns. The poet wants to convey the idea that roses can be tricky.So can love, the metaphor tells us. When one reaches out with absolute trust to touch the object of his or her affection, ouch, a thorn can cause great harm! 'Be careful,' the metaphor warns: Love is a feast to the senses, but it can overwhelm us, and it can also hurt us and cause acute suffering. This is the poet's perception of love—all admonition (劝诫). What is the point?Just this: It took almost 14 sentences to clarify what a simple metaphor communicates in only four words! That is the artistry and the joy of the simple metaphor. According to the passage, what is a metaphor?