Revealing mistake: When the bats invade Dr. Dunwoody's bedroom, you can see the strings on one of them.
Revealing mistake: Phibes' "real" face is a mask. Not only can you see the edges of it around his eyes, but his mouth and teeth look fairly unnatural and like a "solid" piece.
Answer: A psychiatrist is still an M.D., and still went to medical school. Perhaps this one had some knowledge of the case, or was simply on hand to provide assistance.
wizard_of_gore ★