I clean out my shells, put them back into the tank in a clean area. In the morning the shells have been moved around, and some are even half buried sometimes. Maybe mine likes them covered in sand.
Dwable changed shells for the 1st time, picking a spikey one, of which I joking refer to as Dwable: Attack Mode with my friends.

He's already gone back to his original, though.
Proud owner of two precious PPs: Dweeble and Dwable.