There are two important things to notice about the structure of this sonnet. One is that, except for the closing couplet, it consists of a single run-on sentence. The other is that it is built around a single simile, which takes up the seventh and eighth lines. The effect of crowding most of the poem into a single outburst is to leave the reader with a feeling of agitation mirroring the conflicting emotions that accompany sexual lust. Run-on sentences are often the targets of English teachers’ red pencils, but at times such sentences can be extremely effective.

Shakespeare often filled his sonnets with metaphors and similes, as he did in his famous Sonnet 73, in which he compares his time of life to winter, to sunset, and to a dying fire. In other sonnets, however, he deliberately avoids metaphors and similes in order to obtain the maximum effect from a single striking image. This is the case in another of Shakespeare’s most famous sonnets, Sonnet 29, which begins, “When in disgrace with fortune and men’s eyes.” After complaining at length about his miserable condition, the speaker changes his tone entirely and says that, should he happen to remember the friendship of the person he is addressing, his state, “Like to the lark at break of day arising/ From sullen earth, sings hymns at heaven’s gate.” These are two of the most beautiful lines in English poetry, and they are more effective because they are not competing with any other imagery in the sonnet.

In Sonnet 129, the dominant image is contained in the lines: “Past reason hated, as a swallowed bait/ On purpose laid to make the taker mad.” After this—but without starting a new sentence—the poet launches into another tirade, echoing the word “Mad” at the beginning of the next line and rhyming it with “Had” at the beginning of the line after that. These devices arouse apprehension because it seems as if the speaker may actually be starting to rave.

People do not set out poisoned bait to kill human beings. The kind of bait Shakespeare is referring to is commonly used to kill rats: They are driven mad with thirst or pain and run out of the house to die. One of the reasons the image is so striking is that it implicitly compares people motivated by uncontrolled lust to the lowest, most detested animals. Sonnet 129 is unlike most of Shakespeare’s other sonnets and in fact unlike most other Elizabethan sonnets, which are typically full of references to love, the moon, the stars, and other pleasant things. This strange sonnet on lust has a modern, experimental quality to it which foreshadows the cacophony and deliberately shocking ugliness of much twentieth century art.