An animal's yawn is truly amazing- how is it possible there can be so much movement with so much force... once you try to do something like this you too will shake your head in awe.
Errol uses the mouth position to help choose a facial expression. As Errol developed, I realized I might have made the jaw move from further back and be WAY sturdier. As it was, I needed a position sensor for the the movement, but the actual movement was not very much and getting a good signal was really hard. The frame of the jaw actually bent under opening force and the end position was always just a bit out from the last time. I ended up with gearing to move the sensor more as the mouth opened. (By facial expressions, I mean positioning of the brows, snout and ears)
A later addition was the three switches under the chin so you can move your jaw forward and sideways to activate them. But these need to be placed back a bit so you don't hit then by accident when you open the mouth. I did like the idea of tongue switches (like Joe's Blue Mountain fox has), just wanted to try these to see how they worked. (And remember, you can activate a combination of switches to run quite a few different routines)
Typically, there's more work to be done...