It's a strange sensation to feel a shell suddenly start to move around in your pocket and poke you while you're swimming along minding your own business (and stealing someone and their house). I threw three shells back that were apparently inhabited. I started checking more thoroughly before keeping shells.
Then one of the shells walked away.
Once again, I drove down to the quay wall and threw it back. I'm unsure why I didn't instinctively check the other cone shell before I left this time, just in case. When I returned, I checked the other cone shell and, sure enough, there was another tiny hermit crab inhabitant. So I returned another crab to the ocean.
That process got old very quickly. A little bit later that night, I heard a thud in the bathroom. Upon inspection, there was another hermit crab! I told it that I would take it back in the morning. Unfortunately, in the morning I found the shell on top of the shower drain without an inhabitant. It must have crawled out and fell down the drain. That was a slightly sad moment.