In Hamlet, the natural or proper social order has been turned upside down. Nurturing and sustenance have been replaced by destruction and decay: something is rotten in Denmark. Shakespeare encompasses this unnatural state of affairs through metaphors that are associated with food and drink. A thesis concerned with food as associated with rot or drink as associated with poison could be supported with evidence from the entire play.
The unnatural state of affairs is also explored through time, which is "out of joint." This includes the widowed Gertrude's hasty marriage to Claudius. The improperly short period of mourning is indicated with a food analogy, as Horatio comments that the funeral food had barely cooled when it was used for the marriage feast. Here as well, food is a metaphor for sex. Proper social behavior also separates humans from animals, and Hamlet challenges that separation, saying that a man only concerned with sleeping and eating is just a beast.
The multiple instances in which poison arises provide both literal and metaphorical references to the reversal-of-sustenance idea. The entire society, not just Hamlet Senior, has been (or soon will be) poisoned. Hamlet's suspicion that Claudius poisoned his own brother is highlighted in the play within the play—the dumb show—in which the usurper mimes pouring poison into the king's ear; here, it is the ear (not the mouth) that shows that things are out of whack. Gertrude dies of drinking poison, which is appropriate given that her husband died this way as well.