Bilateral Symmetry and Congruency

Here are a few more examples of the curious visual phenomena that occur when the inverse surface of the volume ( the inner skin ) flips to look like the obverse or outer skin. This odd mirrored bi-symmetrical flipping occurs through z axis, (into the picture plane) and is illustrated here more clearly by observing the figure with and without hair. Notice that the form flips toward and away along a transverse axis (3/4 point of view.)
This phenomena is commonly referred to as congruency.

Convex or Concave?

Here, the first figure appears to be facing away looking up to the upper right. The lower figure appears to be facing us looking toward the lower right. They are in fact the same figure with and without hair.