That's a common fallacy.

3 seconds sound clip from the Horror of Dracula (1958) movie soundboard.

You can hear this line at 00:57:26.283 in the DVD version of the movie.

Quote context

[...]

(LUCY SCREAMING AND MOANING)

- Drink this.

- Oh, I'm all right now.

- Drink it.

- Thanks.

- There's so much in Jonathan's diary I don't understand.

- Can Dracula really be as old as it says here?

- We believe it's possible. Vampires are known to have gone on from century to century. Records show that Count Dracula could be 500 or 600 years old.

- Another thing. I always understood that, if there were such things, they could change themselves into bats or wolves.

- That's a common fallacy.

- The study of these creatures has been my life's work. I've carried out research with some of the greatest authorities in Europe. And yet, we've only just scratched the surface.

- You see, a great deal is known about the vampire bat, but details of these re-animated bodies of the dead, the undead, as we call them, are so obscure, that many biologists will not believe they exist.

- Of course, you are shocked and bewildered. How can you expect to understand in so short a time?

- But you've read and experienced enough to know that this unholy cult must be wiped out. I hope perhaps that you will help me.

[...]