Pi states that the common belief that animals in the zoo are unhappy is "nonsense"(16). What response does he give to prove the contrary?

Pi defends the zoo and attacks the common understanding of animals in the wild as free, and animals in a zoo as "unfree", for freedom in the wild is a myth: animals are restricted by their survival needs and their instincts. In the zoo, they live a life of relative luxury not having to worry about survival of the fittest.