The darkness filling the room, the sudden change in Sabre's tone… it clicks in Clover's head. She may be young, but she feels some kind of… vile aura filling the storage, surrounding the desperate pony.
Clover realizes what Sabre is feeling. It's fear.
Clover turns about on her hindlegs, attempting to be quiet as she trots up the stairs, like a sneaky pony should.