Well, a good place to start would be in Chapter 46, which is when the hyena savages the poor defenceless zebra. The description of the violence is very graphic and rather disturbing as the hyena disembowels the zebra and mortally wounds it. Consider the following description:

The zebra's attempts at self-preservation only whipped the hyenea in to a frenzy of snarling and biting. It made a gaping wound in the zebra's side. When it was no longer satisfied with the reach it had behind the zebra, the heyna climbed onto its haunches. It started pulling out coils of intestines and other viscera. There was no order to what it was doing. It bit here, swallowed there, seemingly overwhelmed by the riches before it.

Rather brutal stuff, but what this does is to highlight the plight that Pi finds himself in. Whether you believe that this is an allegory and Pi is actually talking about humans or not, this description serves to highlight the desperate straits in which Pi finds himself and the way that both humans and animals can react with a kind of violent madness to being trapped on a lifeboat with no room to move and others around.