Okay, I tried it. He may already have been dead, but I thought I felt him barely perceptibly pulling back a little when I tapped his operculum. First I tried gently tapping the bubble/sac, with no result. He didn't react at all when I made the tiny pinprick (I used a beading needle). The bubble deflated slowly and he fit back in his shell upright. I guess I was hoping his gill would keep him alive until this could heal; anyhow, I left him in about 1/2" water for a few minutes, and I think his flesh lightened up a bit in color, but now that he's back in the tank, no movement at all. I should know by morning if he's gone for sure.