Early Encounters with Evil (Chapters 1-3)
The first descriptions of Hyde immediately establish him as unnatural and terrifying. When Enfield describes how Hyde "trampled calmly," the oxymoron shows someone committing violence without any human emotion or remorse.
Nobody can quite explain what's wrong with Hyde - he's described as having "something displeasing, something downright detestable." The alliteration emphasises disgust, whilst the vague word "something" shows that his evil defies normal description.
Jekyll appears as Hyde's complete opposite - "a large, well-made man" who seems like the perfect Victorian gentleman. However, his arrogant claim that "the moment I choose, I can be rid of Mr Hyde" shows dangerous hubris that foreshadows his downfall.
Watch Out: The "blackness about his eyes" shows Jekyll's true nature bleeding through - the boundary between good and evil is already weakening.