Puffs of debris coming out of live rock?

[angelapound]

Every once in a while I'll see a little puff of debris come out of my live rock. I've seen it happen in a couple different places, but it's always in the same places. Does anyone know what kind a little critter would be doing that?
Thanks!

 

[bigarn]

it could be a peanut worm burrowing through the rock.