Well, if Jamie's dead, there won't be any yelling. But nothing attacks him before he makes it to the rubble and some better cover. The rubble shifts again, and Jamie raises the rifle, ready to pull the trigger if need be.

And...nothing.

The rubble had just shifted of its own accord - possibly from the vibrations from an explosion, possibly just from gravity.

Once satisfied, he heads back towards Kaylee's hiding place. He actually makes it back there in one piece and opens his mouth, about to give her the all clear.

It's then that the sound of footsteps can be heard, and murmured whispers - but not from the same location. These? Happen to be from directly behind them, just past the other side of the rubble.