"the mother" is written in free verse, so it doesn't have a consistent form, rhyme scheme, or meter. (To get all the deets on this topic, check out our "Form and Meter" section). The cool thing about free verse poems is that they can shift their form at whim.
Reading "the mother" aloud is a bit of an emotional roller coaster. We begin with some sing-song-y rhyming couplets, then they fall apart, then they come back with a vengeance, and then they disappear again (again, check out "Form and Meter"). And all of these shifts in rhyme scheme, in line length, in address—basically, in how the poem sounds—have an effect on our perception of the mother. She seems to be trying to control her words through her rhymes, and we feel as if she loses control as she stops rhyming, then begins again, then stops. When we read "the mother" aloud, we experience the ups and downs right along with the speaker. The unpredictability of the poem at a sonic level places us in the precarious emotional state of the grieving speaker.