How the long O sound looks and how it is made:
The posture of the mouth opens and then ends with the lips close to rounding.
The tongue moves from a low-back position (in relation to the roof of the mouth) to a mid high-back position to produce the sound.
How the long U sound looks and how it is made:
The mouth moves from a open posture position to a lip rounding position as the sound is made.
The jaw does not move.
How the OO sound looks and how it is made:
The jaw is open, and the mouth posture is open as well.
The tongue is raised to a mid-high position, with the tongue pressing into the upper molars.
Lipreading.org