Question

what makes the author refrain from killing the snake ?

Answer 1

this was because of the reason that the snake had not conducted any mistake
it just came to the trough of the poet to quench his thirst.He came to sought hospitality from him.

Answer 2

The poet feels very sorry for his disgraceful unacceptable , and uncouth behaviour or action and rebuked the voice and education and civilization and that had shaped his thoughts are urged him to have chased away the creature. Thus, he says that he has to make amends in his behaviour or change his attitude, deviating from pettiness.