Lower eyelids

Soon a decent post with images, but for now some thoughts on drawing facial-expressions...
I was watching 'The little mermaid' the other day and noticed something I find intriguing: in the scenes where Ariel is animated by Glen Keane, the lower eyelids of Ariel are often drawn. I think it really helped to convey the emotions of Ariel. And what a brave think to do! In my experience it's real tricky to draw the lower eyelids on a girls face: if not done skillfully, the eyelids immediately turn into ugly wrinkles.
Funny enough, in a 'Disney Channel making of - TLM', Glen Keane himself tells us he tried to draw the lower eyelids to push the emotions further and found it a real challenge.