She snorted loudly in surprise when something fell on her back, immediately stopping in her tracks. But whatever fell on her back, never fell off... panic started to set in. At first she tried bucking a few times, then broncking once or twice, but nothing seemed to work. In frustration and fear she let out a shrill whinny, stomping her hoof down before starting to rear, following it up with a strong buck, kicking her hindlegs as far and high as she could. But nothing worked. In panic she started to look around, but there was nothing but walls. "Get off, get off, get off, get off" She chanted fearfully, trying a few more bucks, even though she knew they didn't help. 

In desperation she decided to roll, apart from slamming into the walls, which would be painful and so she'd rather avoid it, was the only thing she felt she had left to try. She laid down quickly, but carefully, the rough stone was not very comfortable on her fragile legs, and then clenched her eyes and started to roll from side to side. It finally seemed to have worked. When she got up, whatever clung to her back, had finally let go. She couldn't make out what had been on her back however, from what was left over on the stones.