The poor things were so confused; they clearly remembered *some* parts of their real lives, and didn't understand why they couldn't do whatever role they'd been forced into. What if they just forgot what cutie marks were for?
Wait what.. I thought the ponys found out teyre destinies aftert hey get the cutie marks, but the cutie marks ARE theyre destinies? Then that means theyre cutie marks are them because its theyre destinies, and when the cutie marks changed they changed so the cutiemarks ARE them But the tatoo changes theyre memories too, meaning that theyre not them, meaning, APPLEJACK, IS RARITY.
The pictures on the ponies' haunches are their cutie marks, which indicate what their special magical talent is and what sort of job/hobby/life goal they'll have. The finale of the most recent season (the episode "Magical Mystery Cure") involved the main characters having their cutie marks accidentally switched around, which completely screwed up their lives because it also altered their personal destinies.
Here's a list of all the episodes in the proper order: [link] ; just go to YouTube and search for the episode title you want, and there will be plenty to choose from. They're all available in HD from iTunes as well.
If we're gonna be *technical* about it, the broad, flat slab of muscle on the side of an equine's hind leg is the *haunch*; the flank is actually just forward of it, behind the ribcage, and connects the body to the leg. If we're *not* being technical, everything above the ankles and behind the barrel can colloquially and collectively be called the rump or the butt.
I wonder how many millions of people think the flank is the wrong part of a horse's ass because a gaggle of cartoon ponychildren got mocked by their cartoon bully antagonists?