The walls of the cavern begin to shake violently.
All around the two mares rocks and rubble tumble down. A deep bellow resides from somewhere deep, deep within the intricate systems of caves. Inside the walls a furious scratching can be heard.
scratch
scratch
....
And then, for a few seconds, silence.
Suddenly the walls appeared to move, but it wasn't the walls moving, but a thousand tiny spiders with bright red eyes suddenly pouring from the cracks created by the minor earth quake.