When Bob says "Yeesh! What a nutjob!" the crown emblem on his shirt is initially missing.
Harold is 3-4 years older than all of his 4th grade classmates, and yet, this episode shows him attending preschool with everyone else.
When Helga initially imagines the lemons as multiple Arnold heads, they are completely yellow and have Arnold's usual voice, albeit slightly higher pitched. At the end, when she imagines the lemons is Arnold again, they are now Arnold's regular colors, and have much lower voices.
When Helga is lying down, one of her pigtails disappears between shots.
After Dr. Bliss says, "So nobody's ever noticed you?", her mouth moves again even though she doesn't talk.
