
How about a few more words on how laughter happens? I'm obsessed with finding out why the cheek enlarges so much, even for a smile as shown above. Mark Mayerson says the cheeks enlarge to accommodate the extra skin which is pushed out of the way by the smile. He's almost certainly right, but...well... where's the wrinkles you'd expect to see if skin was being packed that way? And why don't you see the skin traveling upward in steps, into the cheek?
I really shouldn't pursue this. The answer is probably obvious and I'm just being dense.

Here's a picture (above) that seems to confirm Mark's opinion. The cheeks don't bunch up much, maybe because the skin is spread all over the side of the face. Boy, this face resembles a screaming baboon!

The small picture on the lower left (above) is interesting. It shows the lower jaw receding backwards into the face as the woman laughs. The upper teeth don't seem to move much.

Of course it's an effort to hold a smile very long. You get tired of keeping the cheeks up. When the strain becomes unbearable (above) you stop supporting the cheeks and the meat collapses downward, back into it's home in the muzzle.
I've seen lots of flabby muzzles, especially on middle aged men and Star Wars fans.