How the heck did Vaalack's forehead go back to being somewhat human like....

Alright so when Stiles and Lydia went barging in Eichen house to find the author of the dread doctors, bc Kira and Scott couldn't get past the mountain ash (yeah yeah) then Stiles and Lydia did the who interegation without the flashlight instead a instence stand down, meanwhile Kira and Scott are having "issues" with Kira setting off electricity and all, and then you have the part after Lydia screams as form of payment to the creep doctor... then the Doctors go back in and unscrew Vaalacks eye from his forehead... that doesn't make Vaalack super normal enough to heal himself. I say this because in Lydia's present day scenes Vaalack looks totally normal... Minus the part where it turns into revenge of the body snatchers where the truth is revealed through a car mirror???...