There's a quote attributed to Stuart Gordon, director of
Re-Animator, about how in all those old horror movies, you'd see the monster carry the heroine off into the swamp, but you'd never get to see what he planned to do. That desire to depict what the monster had in mind partly served as the inspiration for the infamous head scene in his Lovecraft adaptation.
Director Guillermo del Toro takes a similar philosophy in a different direction in
The Shape of Water (2017), which he co-wrote with Vanessa Taylor. His heroine, the mute Elisa (Sally Hawkins), and his slimy creature, referred to as the Asset (Doug Jones, naturally), indeed go all the way, a couple of times, but it's played as sweet and romantic instead of disgusting and creepy.
You may be wondering how a human woman and a mutant fish-man can engage in coitus. Don't worry. Elisa helpfully explains the process, through sign language and other hand gestures, to her best friend and co-worker Zelda (Octavia Spencer), in a conversation that runs the gamut from stunned incredulity to curiosity to unwavering support. We should all have friends as cool and understanding as Zelda.