They are not meant to be taken literally and are more of an abstract view of the world- a means of alienating the audience. The characters, especially Hamm, are completely degraded and are pure mind . This implicates that they are constantly thinking another one of the themes of the play, that we cannot escape thought. The relationship between Clov and Hamm is interdependent. Clov relies on Hamm for food and shelter and is obliged to him for taking him in as a child.
Dependence is a definite theme in the play.
Nagg and Nell are also dependent on each other. I think Beckett was trying to emphasize the human need for communication. Even if the conversation is about nothing, people are compelled to converse with each other, which is also a sign that we are constantly searching for reassurance and meaning in life. The point being that if we are talking to someone we have a purpose in life, an identity. The strongest theme in the play is that of finishing which ties in with daily rituals and games.