Original sentence: The Greek here is quite hard to express, but Aristotle seems to be referring to characteristics in the nature of each kind of animal thought to be present in their faces, that he suggests might be analysed for correspondences —
Edited sentence: Aristotle is trying to infer that as man or animal gain new emotional traits, expression can sometimes be conveyed by differentiating his/her own appearence.These emotional traits, however, must be changes in ones natural desires