The ability of onions to produce tears allows Duffy to explore the more painful side of a loving relationship. The onion will cause tears and "make your reflection a wobbling photo of grief". The idea of a deserted lover looking at his or her reflection in the mirror creates a vivid image of the end of an affair. The smell and taste of the onion becomes a "fierce kiss" that will stay on the lover's lips and the silvery white rings of the onion remind Duffy of a platinum wedding ring. Finally, the capacity of onion smells to linger makes a suitable metaphor for the fact that relationships will always have a lasting effect. If the relationship is positive the "scent will cling to your fingers" (that is, to the things you use to touch things), but if it is negative the smell will "cling to your knife" (that is, to the thing you use to do harm).
As a whole, the metaphors used in this poem give us a very good impression of Duffy's thoughts and feelings. Her choice of an onion as a symbol in the first place shows that she is unconventional and impatient with conventional clichs. The idea of an onion, which does not look attractive, symbolising love shows that Duffy does not think love is as soft or as easy a process as is suggested by symbols such as satin hearts. Duffy is not afraid of the physical side of love, "careful undressing of love", but is suspicious of the pain that love can cause, of its capacity to cause tears and "cling to your knife". Duffy would like her relationship to be long term, "possessive and faithful", and is not afraid of its becoming permanent.
Although "In Mrs Tilsher's Class" is less concerned with imagery, Carol Ann Duffy's choice of images seems particularly appropriate and effective. The scene is set in a primary school classroom and many of the early metaphors and images evoke this scene in a simple and effective way. The ability of children to become completely engrossed in narratives is neatly summed up in the first two lines
You could travel up the Blue Nile
with your finger.
The child-sized bottle of milk consumed at break time is described as a "skittle", a word that reminds the reader of both its shape and its associations with childhood play times. The positive mood of the first stanza is also emphasised by the sound of the bell being described as a "laugh".
In the second stanza a few notes of unease creep in. Brady and Hindley, the Moors Murderers, are mentioned but then this impression is erased by a description of them as an "uneasy smudge of a mistake" as if you could get rid of these adults who harmed children like the "chalky pyramids" of a previous lesson. By the end of the stanza the happy mood is reasserted in the description of the sound of a xylophone as "nonsense".
Signs of change and growing up are demonstrated by the tadpoles that change from commas to exclamation marks. Commas indicate short pauses and do not denote an end to anything, but exclamations are emphatic stops. This premonition of change is followed by the rough boy telling the 'you' of the poem about sex, marking a transition to less comfortable imagery. July is "feverish" and there is a "tangible" sense of alarm. These feelings are out of key with the innocent wonder of the early part of the poem and there is a corresponding decline in the child's relationship with the teacher. By the end of the poem, the pent up feelings of the child are expressed in the thunderstorm which "split" open the sky.
Carol Ann Duffy makes few explicit statements about the thoughts and feelings of the child in the poem but by careful attention to the meaning of the metaphors she has chosen it is possible to get a very clear idea of the child's thought processes.