No one has seen them made or heard them made, But at spring mending-time we find them there.
We get a bit distracted by all of the bunnies and the dogs, and we hear a lot of barking and shouting in our heads. We keep thinking of the hunt scene from Mary Poppins – you know, right before she sings "Supercalifragilisticexpialidocious?"
Our speaker, sensing our sensory overload, steers us back on course. At the end of line 9, he says, "the gaps I mean," reminding us of the matter at hand (the broken wall), and reminding us about the mysterious Something that destroys this wall.
The Something is very different from the hunters and their dogs (the speaker knows all about them). The Something is far more covert. In fact, it’s so covert that no one sees or hears it make gaps in the wall.
The speaker says that, in Spring, "we find them there." Who is "we?" Is there yet another character on our hands?
Well, at least, now we know when mending-time takes place: the Spring. That makes sense to us. Spring is a time of spring-cleaning, April showers, and little birdies chirping.