One in a brickyard so deep he could not see his reflection (sound is prominent here)
One in a ditch where he had to pull weeds aside to see down (sense of touch prominent here but also vision)
One where a rat dived out of the undergrowth into the well (images and sounds clearer here but an ominous note is sounded with the appearance of the rat)
Tidy regularity but without constraint, with stanzas recalling experiences of childhood and the final one bringing his taste for wells into the present
Wells and fascination with them as a metaphor for Heaney's adult role as a poet, with the rat reminding him that writing poetry is not without its dangers and dark side