Seems that many of the vegetarian species are, in certain times and situations, not entirely vegetarian. Gnawing on other animals and, sometimes, actually actively killing things. And Dumbo may not be above eating people.

http://scienceblogs.com/tetrapodzoology/2010/12/carnivory_in_cows_and_deer.php

The lesson here is that nature does what it must to survive. Don't narrowly define what you can or will eat. Think outside the box. And don't to casually turn your back on 'safe' animals.