The situation of pouring poison in a person's ear narrated in "Hamlet" has the symbolic meaning of contaminating a person's mind by telling them lies that mislead them into situations or actions that are incorrect or are against morality.
This symbolic meaning is the same used in the Bible when the snake, which represents the Devil, shows up in The Garden Of Eden and talked to Eva about the tree of the knowledge of Good and Evil and confused her with lies until she was manipulated to do what was consider incorrect or against the better judgement.
