idk if i've remarked here that del Toro is very good at putting seemingly incidental details to further use, reincorporating them later in the film in various fashions, but this film included a very clear multi-part example i liked.

1. at the start of the film there's a moment where Elisa masturbates in her bathtub as part of her daily pre-work routine.
2. a while later, she's eating cornflakes and her neighbor makes a joking reference to their having been invented to discourage masturbation (my impression is that this is not in fact true and that unlike Graham's, Kellogg's ideas about diet were separate from his campaign against masturbation), which he remarks didn't work.
3. much later, when she breaks her beloved out, she keeps him in her bathtub, which due to the reemphasis of masturbation by the corn flakes joke, now reminds us of that initial masturbation in the tub.
4. soon thereafter they fuck in the bathtub.