"Wait.  Look."  Forgath and Puffy paused, turning back to where Plump gestured down with a hoof.  The pair looked for a moment, until a frustrated Plump Helmet gave the ice a tap with a hoof, cracking the upper layer and revealing a thin trickle of water running along the rock beneath.  "It's gotten warm enough that the ice can melt and flow freely down rather than just creeping.  The next one could be it."