I love studying alternate cultures and in all the reading I've done it is the strange way humans in captivity react that has always fascinated me.
Another is the affect of diet on humanity their size and body mass can vary greatly because of this, just look at the differences between the Nobility an Peasantry of the Dark Ages
Bred an raised slaves in such a society would naturally be of a larger body type because of a better diet during their developing years. That in an of it's self would cause the true slave to see themselves as superior to humans that have to fend for food by other means