Line by line is a little difficult, but I will explain each stanza. This poem takes place in Sicily, an island in the Mediterranean Sea, near Italy.
Stanza 1: A snake comes to the watering trough for a drink. A "trough" is a wooden or stone open container for holding water . It is a hot, hot day and the man is wearing pajamas, which are light, because of the heat.
Stanza 2: The man waits under the shade of the carob tree with his pitcher to gather water. He waits a while which is shown by the fact that the word "wait" is repeated. He waits because he has to avoid the snake.
Stanza 3: The snake came out of a hole in the earth wall. He describes the snake as "yellow brown" and "soft bellied" with "straight gums" and a "slack long body". The snake drinks silently from the tap or faucet.
Stanza 4: There was a second person there waiting with him. They BOTH are waiting and avoiding the snake.
Stanza 5: He compares the snake to cattle. The snake lifts its head, looks at the man, flicks its tongue, thinks a moment, and then goes back to drinking at the faucet. It is a hot day in Sicily, and Mt. Etna, a famous volcano in Sicily, is smoking. Everything that he has learned has taught him that he must kill the snake because in Sicily, a black snake is safe, but the gold ones are full of venom and dangerous.
Stanza 6: Everything inside him says, if you he were a man, you would take a stick and kill the snake.
Stanza 7: But, he likes the snake. He was happy that the snake was his guest who had come to his trough to drink and left peaceful, satisfied, and thankless and gone back to its home in the earth.
Stanza 8:The man wonders if he is a coward for not killing him. Or was it wrong that he wanted to talk to the snake. Or was it respect because he felt so honored that the snake had visited his trough. He repeats that he felt honored.
Stanza 9: The voices from his knowledge of how to handle a snake keep haunting him with "If you were not afraid, you would kill him"
Stanza 10: He admits that he was afraid of the snake, but he was honored more that the snake should seek his hospitality from out of its dark hole.
Stanza 11: When the snake finished drinking, he lifted his head as if he were satisfied, flicked his tongue seeming to lick his lips, and looked around, and then climbed back to his hole very slowly.
Stanza 12: The snake put his head in the hole in the earth wall and slowly drew in the rest of his body. The man felt a kind of protest at his leaving now that his back was to the man.
Stanza 13: He put down his pitcher and picked up a log that was not easily handled and threw it at the water trough.
Stanza 14: The man doesn't think he hit the snake. But suddenly the part that still visible wiggled and pulled itself quickly into the hole. The man stared with fascination. It was twelve noon and the heat was intense.
Stanza 15: He immediately regrets his action as a mean thing to do. He hates himself for it and what society has taught him to do.
Stanza 16: He thinks of the albatross in Samuel Coleridge's poem "The Ancient Mariner" and how the sailor felt guilt at killing the albatross, and he wishes that his snake would come back.
Stanza 17: He thinks of the snake as a king in exile, who needs to take his rightful place and be crowned again.
Stanza 18: He feels he missed his chance to meet one of the "lords of life" and he has something to apologize for, his own lack of consideration of the snake.