These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
In "You Promised!" during the brothers' race at the end, the music is almost exactly "I'm a Believer".
Uncanny Valley: Some of the human designs in the show can range from pretty goofy to downright frightening. For a comparison as to how wildly these models can vary, take a look at this scene◊ from "Beach Beavers A Go-Go", where an example of a character that can easily pass as Fanservice is quickly followed by the appearance of a freaky woman that looks more bird than human.
Stump himself can fall into this, due to the unnerving expression permanently carved into its face and the fact that everybody treats it as if it were alive and sentient.