Rainbow Dash's tone had let Fluttershy ignore the number (and, to be honest, mathematics was never her strongest point), but then Spike had to point it out.

Fluttershy's face falls. Less than one, she thinks. I did terrible. I... I can hardly fly. And as if it just happened, all the taunts the other fillies had sent at her at flight camp, all the weight of their gazes, come rushing back.

She feels as though she can hardly breathe. She starts to run away, sobbing.