Now that I know that they have special lights to put just the right glint in their eyes, I no longer think anything in film is just an accident! - Everything was part of the plan! - Though I did not notice what you spoke of... I may have to see it again!
"special lights to put just the right glint in their eyes"
Considering the special effects they have, I suppose darkening a mouth interior is no big deal.
Yes, we should all probably go see it once more, to make sure we didn't miss something ;^)