How many grains of sand?

Recently one of my friends used "all the grains of sand" as an example of an infinite set "because it is impossible to count them all" and -- even as I rejected his answer -- I wondered how many of my other friends might agree with it.  In the following poem, mathematician Pedro Poitevin considers a similar question as he reflects on the countability of the birds in the night sky.

       Divertimentum Ornithologicum      by Pedro Poitevin

                              After Jorge Luis Borges's Argumentum Ornithologicum.

       A synchrony of wings across the sky
       is quavering its feathered beats of flight.
       Their number is too high to count -- I try 
       to estimate it but I can't:  the night
       is dark, the birds are black, my eyes are weak.
       Certainly less than N but more than k,
       I tell myself, but then, in an oblique
       arrow of thought, I argue with dismay
       that if k is too small, then k + 1
       can't be enough, and so, inductively,
       all of God's natural numbers fail -- there's none
       determining how many birds I see.
       I entertain that He might not exist,
       but N being hyperfinite I resist.

Poiteven's poem was published in 2011 in The Mathematical Intelligencer (Vol 33,  no 4, p 3) and I heard him read it in 2012 at a JMM Poetry Reading. 
     For many years, the Intelligencer has published math-related poetry -- its editors (including Honorary Editor and former Editor-in-Chief, Chandler Davis, and current Editor-in-Chief, Marjorie Senechal, and Associate Editor, Gizem Karaali) all engage in creative writing as well as mathematics and are strong supporters of the arts.
     Another of Poiteven's poems, "Elevator Speech" may be found here in the Journal of Humanistic Mathematics, and JHM is another rich source of poetry with connections to mathematics.