Whether or not the eerie elements of "Dr. Heidegger's Experiment" are actually supernatural is subject to debate. It's a question of theatrical showmanship vs. genuine superstitious belief. The theme creates a mood of doubt and forces the reader to ask some difficult questions about the nature of reality – at least as defined within the narrative. It also severely complicates our understanding of the title character, who has at least one foot in a sinister, supernatural realm.
Questions About The Supernatural
The narrator says that all of Dr. Heidegger's dead patients stare back at him when he looks into his mirror. Does this mean that Dr. Heidegger is responsible for all these deaths? Does it suggest a sort of guilt? What do you make of this cryptic line?
Similarly, what's the deal with Heidegger's dead fiancée? The narrator is rather ambiguous in describing her death. Are we meant to understand it as an accident, or the fault of Dr. Heidegger?
After the four guests have all been "transformed," in one sense or another, the three men fight over the widow, and we catch a glimpse of their reflection in Dr. Heidegger's mirror. The narrator tells us that the mirror reflects them as old people, not as the young people they now believe themselves to be. What do you take this to mean?
Chew on This
Hawthorne condemns Dr. Heidegger for playing God.
Dr. Heidegger's character is both venerable and Godly. Hawthorne paints him as an admirable, if other-worldly, figure.