In reading this poem, I tend to follow the prompt in the opening line and enjoy Sylvia Plath's poem "Metaphors" as a riddle of sorts. I think that reading the poem in this way may very well help you discuss it in terms of denotation and connotation. The images of the poem center around the speaker's pregnancy -- she's, among other things, "An elephant, a ponderous house, / A melon strolling on two tendrils."

The denotative value of each key word is the dictionary defintion. An elephant is a very large mammal; a melon is large and round, tendrils are curling vines, etc. The denotative meanings are important, but they're not enough by themselves; the images seem unrelated. The connotations are what allow for a second, richer meaning to emerge. The speaker does not seem all too overjoyed to be pregnant. Many of the images in the poem convey a negative connotative meaning, such as unpleasant fullness or ripeness.