I have two Chinese Mystery snails (I just unloaded 5 yesterday). They look like they sneeze, most often after a water change, sometimes not. Usually their shells lurch forward quicky, and they recover, then it happens again another 2 or 3 times. They go for a few minutes wihout doing it, and then they do the cycle again. They aren't doing anything special beforehand, just eating or "looking" for a gnosh. It's striking me as a signal of stress/sudden change. They "hole up" when the water's not great (I don't think I need to test my water anymore if I watch the snails.... but I will anyway.), they're still out and about, and I've tested my water and it's fine. Any ideas? It's really cute, but it looks uncomfortable to get bonked on such a soft head with a hard shell in the middle of breakfast.