[Invisible meshes work in the background of all images tirelessly.]
[The weight between meshes and the movement of their corresponding bones]
[The correlation between the eye and its corresponding IK bone's movement.]
[The correlation between the 'nose' and its corresponding bone's movement.]
[The correlation between the 'mouth' and its corresponding bone's movement.]
[The correlation between the hair and its corresponding transform bone movement.]
Illustration @sevg3lart