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.
Ear Worm: The animated series is chock full of these.
Nightmare Fuel: It's not a particularly scary book in the traditional sense; Harold is a little boy who draws things with his crayon and they come to life, and they're almost exclusively nice things. The creepiness comes later when you realize that Harold is the only real character in the book. The whole world is empty, except for Harold and his crayon.
Averted in the animated series who starts and ends in the Harold's room, with an art shift to make it clear what happens in Harold's imagination and what happens in the real world.note things happening in Harold's imagination has a purplish tint as it is drawn using the purple crayon. Also, Harold's parents are often mentioned and his mom (although only her hand is visible to the audience) appears at the start of the several episodes to joss the fact that Harold's alone in the world.