Kryptoknife

See, see, where Christ's blood streams in the firmament! [Doctor Faustus]

Superman, Superman and Superman!
Thinketh, he dwelleth i' the cold o' the moon!
His heart is his weak spot, the organ
upon which kryptonite has most purchase.

Superman's blood is packed with corpuscles
each blood cell is superpowerful:
undying blood, flowing faster than a train
propelled by a heartbeat pulsar-quick.

Now he sits in the lunar quiet. No need for air:
his lungs work and superwork, but not
to transfer oxygen to the superbloodstream.
His red-blood-cells aren't haemoglobin-red.

They're red as Martian weed is red, as red giants are.
His blood red-shifts as it flies streaming past us
(he has taken a kryptoknife and cut into his arm)
a snaking line of red, shallow-curled in an S.