I had a little scarlet hermit traipse onto a cap frag. It wandered about in the usual blundering fashion, picked up some aragonite that had gotten blown up onto the frag, took a few other picking bites, maybe at detritus. And about the time I was ready to intervene for the sake of the frag, the crab suddenly collapsed, bump! face-forward into its shell and stayed there a moment. It made several attempts to get up, finally got to an edge and got down, but did not move too far for a while, then wandered off perfectly fine. I'm wondering if that coral has defenses that aren't evident to the human handler.
