Shortly after the humans had flown from RD's mouth, another human duplicated her and tricked both into going to Sugarcube Corner, at the same time.
The RDs walked into the store, side by side, unwittingly. They didn't notice each other, due to the fact that the human had disguised them from each other. It was fairly effective on them.
Pinkie Pie was another story, because, she turned around at the voice of RD, and almost exploded. Twilight and the others were at the other end of the store gaping.
"Hey Pinkie!" The RDs said, in perfect unison. They still hadn't noticed each other. "I'd like a few cupcakes."
Pinkie suddenly grinned wildly and grabbed a few cupcakes, handing them over to the RDs. They took them as Pinkie squealed, "YAY. MORE FUN WITH RAINBOW!"
The others were still gaping when Spike fell to his knees, "DOUBLE RAINBOW!?"
Twilight dropped down to and screamed into the sky, "WHAT DOES IT MEAN?"
The RDs saw each other and fainted while Pinkie jumped around happily. The rest of them were stuck with their mouths open while the Human put many many carrots in their mouths one by one.