Modern theories for the formation of structure in our universe predict that galaxies are embedded in giant balls of million-degree gas known as "halos." Telescopes are only now beginning to probe these halos, and have unexpectedly found cold gas precisely where we expected it to be hot! Such cold gas presents serious problems; among them, it does not have enough pressure to hold itself up against gravity. I will explain these puzzles via a new “shattering” instability, which fragments cold gas into tiny pieces. These cold gas fragments disperse throughout the halo, much like the water droplets in a fog.