Corrected entry: The outer layer of human skin is bonded to the subcutaneous layers beneath. When Raine is cutting the swastika into Landa's forehead at the end of the movie, the extreme close-ups reveal that the "skin" is a thin layer of rubber attached to a blood pack - you can see the edges peel up as he is making the incisions.
Gibbsdoc
7th Sep 2009
Correction: This is true for most skin, except the areas of the scalp and forehead - because of the unique nature of this skin, there often is more mobility and separation between these layers than in other areas of the body. I have watched these scenes again, and, as someone who has made incisions in these areas, I have to say this looks very realistic.
Gibbsdoc