I am a bit stumped. I finally carefully surveyed several of my clients last week because I have been told several things about this issue. Five people told me that, yes indeed, "oreja" was the word for the ear of an animal and "oído" was the word for the ear of a human. However, two people told me that this was not correct. They said that the oído was basically the inner part of the ear and that the oreja was the outer part. They said that animal vs human had nothing to do with this oreja/oído thing. My son said the latter also. He is studying Spanish in grad school but his Spanish is really Spain Spanish. One of my clients who had the latter position told me timidly that probably the people who claimed the animal/human distinction were not very well educated. The clients that I am mentioning are all from Mexico. I don't know if there could be regional differences within Mexico related to this issue. I would really like to feel some certainty about this since I am always yapping to little children about this body part.