Dr. Frankenstein was a mad scientist. It's right there in the name: "mad."
And we don't mean angry. We mean insane. Nutso. Cuckoo. A wack-job. A crackpot. Certifiable. There are so many more words for insanity and madness than there are for "normal," probably because being crazy is a) a lot more interesting and b) a lot more common than people want to admit. Madness is the new normal in this film.
Questions About Madness
Is Frederick crazy at the beginning of the movie? What prompts him to go mad, or do you think he remains sane throughout?
What other characters would you consider "mad" and why? Is anyone in the movie "sane" or is everyone in an absurdist comedy crazy in some way?
When Frederick is proven to be "right" (i.e. the monster is shown to be civilized) does that make him any less crazy?
Are people, like the townspeople or Elizabeth, crazy for accepting the monster as normal in the end?
Chew on This
The characters who should be sane and normal—like the doctor or the inspector—are the craziest, whereas those you'd think would be crazy, like Igor, are actually a lot more mentally stable and in control of themselves.
Madness is all relative. Everyone in this movie is completely nuts, therefore, in the context of this crazy film, they're all 100% sane. The film explodes the distinction between sane and insane.