Why is the tiger angry? Why does he express his anger quietly?

Please answer the question in about 30-40 words.
My question is from the book 'First Flight' and from Chapter-"A Tiger in the Zoo".

Dear Student,

The tiger is angry as he is trapped in the cage instead of roaming in the wild. As he is trapped in the cage, he cannot express his anger with ferociousness. Thus, he is forced to express his rage quietly.

Regards,