no layer = worm
layer 0  = shells
layer 1  = bullets, realy fast moving objects
layer 2  = big hard pieces -- not on flame
layer 3  = small hard pieces -- not on flame
layer 4  = big soft pieces
layer 5  = smoke
layer 6  = energy, fire
layer 7  = destroyable, but not pushable
layer -1 = blood,smoke,trails, not used for affecting an object

custom_event(1) = burning