When the other Elements of Harmony realise that Fluttershy gave each of them a different reason for not attending a slumber party, they set out to discover the truth.
They end up discovering something else instead.
AUTHOR'S NOTES: This story was inspired by a blog post that Obselescence wrote — although I should point out that it has absolutely nothing to do with the idea he suggested (hence the lack of a 'Romance' tag).
Rated T for innuendo.