No, I didn't miss that, and I disagree that it's either subtle, or a joke in itself. It's all part of the same big, unsubtle joke of 'the kid scares the monster, because he likes vore and wants to be eaten'. Liking Jaws is foreshadowing, the not-so-Kuchisake-onna looking like a shark allows the joke to work, and relating the two of them allows the joke to build for proper pacing.