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.
YMMV: My Little Pony: Friendship Is Magic S2 E6: "The Cutie Pox"
Ensemble Darkhorse: In a fandom where every background pony will be named and characterized, it took only a few hours for the community to come to agreement on the name "Allie Way" for a oddly-taller pony in the cold open and fanart to appear. Whether she is related to Vinyl Scratch (due to the similar blue-striped hair and both being unicorn ponies) or Snails (due to the lanky appearance) still seems up in the air.
The seeds of truth grow when you tell the truth and only Apple Bloom's truth does the trick. This is likely because Pinkie Pie wasn't telling the truth. Note her erratic behavior during her confession. Who's to say that she ate more than six corn cakes? Who knows? She may have even eaten *gasp!* a dozen!
Alternatively, Zecora could have enchanted the seeds to respond only to the truth from Apple Bloom, since it was clear from the outset that the filly's pilfering was what brought Zecora to town. She might have even enchanted the Heart's Desire to give Apple Bloom the symptoms in the first place, just to teach her a lesson in patience.
Nightmare Fuel: An ailment that gives you genius ability but that forces you to perform it indefinitely is a trope that has been used in other works with rather gruesome imagery, including Hans Christian Andersen's "The Red Shoes", the Looney Tunes short, "The Wearing of the Grin", and the Buffy the Vampire Slayer episode "Once More With Feeling".
It also occurs in Real Life under the name of "Dancing Fever". In an eerily similar parallel to the original Cutie Pox pandemic, a town in France was wiped off the map by Dancing Fever in 1518. Also like Cutie Pox, Dancing Fever has no cure.