Mr. Biswas will "eat up his mother and father" (Metaphor)
When Mr. Biswas is born, the pundit prophesizes that he will "eat up his mother and father." This probably is not a hypothesis that Mr. Biswas will become a cannibal: rather, this is a metaphor portending that Mr. Biswas will consume all of the resources of his parents, which is part of why his birth is seen as an ill omen.
Paddler (Metaphor)
Seth and the rest of the Tulsis give this nickname to Mohun as a sarcastic allusion to Mohun's statement "paddle your own canoe," a metaphor meaning that everyone had to paddle through a river of hardships to make it big in the world. They taunt Mohun for his many failures, despite all his effort, by calling him this name.
Catching Crabs (Metaphor)
Catching crabs was considered one of the most low-paying jobs, and is often used as an insult to imply the social status of someone. The derisive quality of the metaphor, beyond the literal insult of crab-catching being a menial job, comes from the implication that certain people are only fit to catch and deal with "bottom-dwellers" (i.e. crabs).
The Hunt for a House of One's Own (Metaphor)
Mr. Biswas' intense, lifelong desire for a house of his own is more than a literal desire for a place where he can live: it's a metaphor for the deep desire many of us feel for self-determination in a modern world that often makes people feel as if their own lives are largely out of their control. The tragic irony of this story's structure, in this regard, is that the titular character—the one around which the entire narrative should presumably pivot—is apparently doomed to be defined and determined by the other people in his life, rather than himself.
Mr. Biswas' Extra Finger (Metaphor)
Mr. Biswas' extra finger is one of the reasons why he is seen as a misfortune from the very moment at which he is born. In this way, Mr. Biswas being born with an extra finger is a metaphor for how many people are judged and persecuted their entire lives due to aspects of their birth (e.g., race, socioeconomic status) that are entirely outside their control.
