In Chapter 1, as he journeys to Castle Dracula for the first time, Jonathan Harker uses both hyperbole and simile to describe Transylvanian superstitions:
I read that every known superstition in the world is gathered into the horseshoe of the Carpathians, as if it were the centre of some kind of imaginative whirlpool; if so my stay may be very interesting (Mem., I must ask the Count all about them.)
Obviously it is not the case that "every known superstition" can be localized to this small portion of the world, and though it may be an "imaginative whirlpool" (as in Harker's simile), it is not the center of all superstitious imagination. This is exaggeration for effect; by using hyperbole and simile in this manner, Stoker primes the reader to associate Transylvania with strange and otherworldly phenomena. Note that fear of the unknown or foreign is common within the characters' narration and dialogue, hinting at broader social/cultural fears in England centered on "aliens" or "non-native" entities.
It is also important to note the dramatic irony in this passage. Readers in the 21st century are aware that Dracula is a vampire before even reading the novel, since the character has become culturally ubiquitous. Though Stoker may not have originally intended this passage to be ironic, contemporary readers will comprehend the irony of Harker wishing to ask Dracula about local superstitions (of which he himself is the subject).
