Pinkie Pie gives Fluttershy a new treat for her breakfast, a packet of lime flavoured jelly cubes. However being to hungry to wait for the water to boil, Fluttershy decides to take a quick nibble of her new treat.
The results of eating a packet of lime flavoured jelly cubes while writing.
Jelly = Gelatin for Americans etc. Pinkie mentions it during the story in her own special way.