[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