When Rainbow and Fluttershy are travelling to the mountains of the yaks to do an important royal duty Twilight has given them, one bad thing happens.
They get hit by a storm and land in a cave on a mountain to regain their strength. A wing broken... and the cold setting in.
And when the next morning the worst happens, Rainbow Dash is left with a choice that no pony, no creature, should ever have to make.

To eat... or starve...

But she makes it...

But Fluttershy doesn't.