The tiger is imprisoned in a concrete cage. IN THE CELL, THE TIGER IS MOVING. The cage's few stairs are insufficient for tigers roaming the woods. The poem also mentions that he is measuring the length of the cage. This means that the cage is not square but rather longer than it is wide. Tiger lives in the forest. In order to survive, he must hunt and eat other animals. He does not do this because he wants to, but because he has no choice if he wants to live. Even though he is a big cat, capable of killing large animals with his claws and teeth, he cannot go out into the world alone because then he would not be able to find food. So he stays in a small space for as long as possible so that he can catch his prey quickly and escape back to the forest before anyone finds him. This description comes from a natural phenomenon called an "animal trap". An animal trap is when two different habitats share a boundary: for example, a pond and the field next to it. If an animal crosses the line from one side to the other, they trigger some kind of trap which closes behind them, trapping the animal inside. Scientists use these traps when they want to study certain animals without harming them.