Finally, something tangible to show!
I have completed the main section of the breathing mechanism for the Martian. At its heart is a threaded bolt which causes a wing-nut to move back and forth when the bolt is rotated. This wing-nut then pushes out two hinged arms on either side. An elastic band connecting the arms then pulls them back in when the direction of the wing-nut is reversed (by rotating the bolt the other way). In practise, I suspect the elastic sides of the animation puppet would push the arms back in without the elastic band, but it's there for the video demonstrations below.
The mechanism is incomplete, insofar as it would have to be attached to a pair of 'breast-plates' which will conform to the shape of the Martian's body. The basic mechanism as shown could also be used in puppets of quadruped creatures, such as certain herbivorous dinosaurs.
To give an idea of size, the threaded bolt is around three-inches (75mm) in length, and it was animated with one complete turn of the bolt per frame, at 25fps.
The basic mechanism is shown, as viewed from above, in the schematic diagram:
And this video shows the mechanism's action:
While this one reveals the inner part of the mechanism, with the arms hinged out of the way, just about showing the piece of square plastic epoxied to the wing-nut which prevents it from turning and losing contact with the hinged arms: