I'm not sure if mine was just weird, but the first time I spoke with Parthunax on the mountain, he slinked low with his head on the ground looking up at me. It reminded me of nothing so much as a subdued dog - subservient to its master but looking up hoping you'll drop a bone or something.
Does he always do this? I figured he should tower over me looking badass instead of this...

Oh and the way he was moving his mouth made it look like he was mumbling.