Help ID Please!

[LearningtoFish]

My friend added a piece of liverock to her tank the other day and these two guys popped up. When she tries to touch them they shrink back into the rock.

Any idea what they might be?

(Sorry about the quality of the picture. The camera on her phone couldn't get it any clearer.)

 

[iretthepirate]

Can't really tell from the pic sorry but if she's worried kill them