How we cite our quotes:
A man lives in the house he plays with his vipers he writes (line 5)
This line almost sounds like it could have been written by a child, doesn't it? But we learn so much about the identity of the guard. He's like an ordinary, middle-class guy, but he has a sinister side, what with his vipers and all. He's also a writer of some kind, so he must be cultured. One of the lessons the Holocaust taught is that people can do monstrous things without seeming like monsters most of the time.
he whistles his hounds to come close
he whistles his Jews into rows has them shovel a grave in the ground (lines 8-9)
Celan uses parallelism in these two lines to compare the Jews with animals (hounds), which is exactly how the Nazis thought of them. They are like possessions that do work for him, just like his dogs. And calling them "his Jews" emphasis the role of "master" that is explored later in the poem.
Black milk of daybreak we drink you at night
we drink you at morning and midday we drink you at evening
we drink and we drink (lines 11-13)
These lines, repeated at the beginning of each next stanza, are practically the only use of first person in the poem. The Jews do not have an identity except as this mass, uniform group that must suffer together. They are like ghosts or the ghostly chorus of a Greek tragedy. And yet we learn about these speakers through the use of tone, especially irony, and by the small details that they notice, like the guard's blue eyes.