There's a nice little feature on the Lady and the Tramp dvd

[auburngrad82]

It's a restored episode of the Wonderful World of Disney showing the making of Lady and the Tramp. In it, there's a short spot where Frank Thomas does some simple pencil animations of the facial expressions of the canine characters as they talk. They also show him using a mirror to watch his mouth move as he spoke the words. Then he drew the dogs' mouths to work like his did. It's a nice little inside view of how the animators at Disney worked.