The Click of a Sundial

Billy Collins is one of my favourite poets, his poems are easy to read yet often contain surprising views of everyday experiences. I have recently started reading his book Picnic, lightning which was published in 1998. Yesterday morning I read the poem Picnic, lightning and loved the final stanza:

and all I hear is the rasp of the steel edge
against a round stone,
the small plants singing
with lifted faces, and the click
of the sundial
as one hour sweeps into the next.