Fluttershy: "Thanks for the foot massage little bro. Now on to the next thing."
Zephyr: "So sis, why'd you grab and put me on your butt again?"
Fluttershy: "I exercise as much as I can and my butt keeps jiggling around when I move a lot and I'm trying to reduce it as much as possible so I can exercise without distractions. I need you to stay on big sis's rump for a bit to see if anything has changed (giggles)
Zephyr: " Two things: one, you need to lay off of the cupcakes sis. And two…I don't think that's why you brought me to your room. Your butts big so it'll jiggle while you move regardless of what you do. Why didn't you ask Rarity for something like this?"
Fluttershy: "Because we never really spend too much time together as siblings so here's a great chance to do it my dear brother. It's time to start so hold on and sit tight k?"
Zephyr: " (gulp why am I doing this? It…it's for my sister so as her brother I'll really need to restrain myself…but seriously why directly on her butt O///O
I edited out Fluttershy's wings to focus more on the big picture.