(Video: a Variety of Visual Illusions) as a Mask of Charlie

(Video: A variety of visual illusions) As a mask of Charlie Chaplin's head is rotated, the nose in the hollow back of the mask seems to be sticking out. In fact, it is sticking in. This illusion happens because

A) of retinal disparity.
B) of your vestibular sense.
C) we experience perceptual constancy.
D) a hollow face is so unlikely our brain refuses to see it that way.