Goofs

When Dr. Carruthers go to release the giant bat the first time, there are several glitches that turn the screen black repeatedly; also 5 bats come out before the huge one. But there was only the huge one when the good doctor was in there.

Although all the bat attacks occur at night, much of the footage of the bat flying to and from its destinations was clearly shot in the daytime.

At 8:30, when the doctor is in the lab "feeding" the bat the fragrance, the bat's head and body are all black. In the stock footage cutaway to the closeup of the bat, the bat's body is white.

Director Jean Yarbrough's name is misspelled as Yarborough in the credits.

Reporter Johnny Layton tells Dr. Carruthers that he'll protect the doctor from the second Devil Bat in order to save him for the hangman. But, by the time this film was released in Dec. 1940, every state in the continental United States had switched to the electric chair as capital punishment for murder.

When the reporter wrestles the doctor to the ground near the end of the film, their feet clearly wrinkle the fake grass on the set.

In the lab scene, when Tommy tries to flick a drop of the deadly lotion on Dr. Carruthers, he flinches away and says he has a violent dislike of perfumes. Immediately afterward though he shakes Tommy's hand which has been slathered in the lotion.

After Johnny Layton (Dave O'Brien) shoots and kills one of the devil bats, the article in the Chicago Register states his name as Henry Layton, while another one in the Springfield daily correctly names him as Johnny.

Throughout the movie, references are made to Illinois locations (Chicago, Peoria, Springfield), yet the scenery shown at the beginning of the movie is clearly Californian.