“It survived only by moving.”

The shark is an elemental force which greatly predates humanity. As such, the humans are a mere blip on the radar of a creature which has been evolutionarily unchanged for millennia. The humans are dealing with a killing machine which is an expert at surviving and moving forward.

“Summers were bad times for Ellen Brody, for in summer she was tortured by thoughts she didn’t want to think—thoughts of classmates now married to bankers and brokers, summering in Amity and wintering in New York.”

Ellen is “tortured” by the idea of the life she might have led if she was not bound to Brody and Amity. She dislikes what her presence in Amity says about her: That she was not smart or strong enough to survive in the big city. Summers remind her of the diminished ambitions of her small-town life, creating within her the desire to explore the alternative life she could have had.

“The stink of vomit reached Brody almost instantly, and he knew he had lost his struggle.”

Brody cannot maintain control of his body’s natural disgust around a corpse, despite his best efforts. The struggle against the self to maintain control will continue to haunt Brody as he fights against the external, elemental force of the shark and the internal, human paranoia which festers in his mind. The world sickens Brody, and he struggles to keep control of himself in this difficult time.