If you were to show one cel to represent

With any luck, Yue's gaze would convey what I'm forbidden to say.

http://thingswithwings.rubberslug.com/gallery/inv_info.asp?ItemID=32562

While this isn't my favorite, I think it conveys a lot of mood and emotion, despite my crappy scan:

http://onihime.rubberslug.com/gallery/inv_info.asp?ItemID=68766

I don't think I'd have to say another thing.

I'd definately show a cel from CLAMP as an example of an animation cel. Here's one I'd show from X/1999 of Hinoto:

http://rheytarian.rubberslug.com/gallery/inv_info.asp?ItemID=55556

I would have to use this one.

http://catgirlsandbeauties.rubberslug.com/gallery/inv_info.asp?ItemID=39412

It's from Plastic Little and you can really see the ability to show emotion (I can't spell late at night) by how the eyes are painted. If I could have more than one, I would have to go with my "Now and Then, Here and There" Cels.

ONE???? I suppose it would be this one.
http://thistledown.rubberslug.com/gallery/inv_info.asp?ItemID=65027
but ask again tomorrow and I might have a different annswer ^_~