Possible Clues:

• Under the skin it's the wrong way for Mister to be inside the side
• The skin layer below the surface
• Mister turns skinny inside the side
• Skin below the outer layer
• Blunder mismatches some skin
• True skin below outer layer
• Skin overly inflamed? Mark exists
• Visibly embarrassed about short girl's skin
• Collagen container
• Inner layer of the skin