I think that is a piece of undigested cuttle bone.Ok thanks!! I'll do that! I don't see them during day unless I go out there and they come to greet me. They do love the rain! I have a hose running through the middle of their areas that goes on for 1-2 minutes every hour. Everything pretty much stays damp. Since you have redfoots, my cherry head passed some gritty white/yellow toothpaste like stuff yesterday. He's did this a couple of years ago and I increased his soaking and it went away. I haven't been soaking him as long because as soon as I put him in the tub, he takes a huge drink and then constantly tries to climb out. I soak them 3-4x week. I'm going to soak him everyday for about 30 minutes. He does eat cuddle bone and I put calcium on his food about 2x per week. I came home today and there was a rock/crystal looking thing on top of the coco coir in his house where he was. Now I'm freaking out and I'm afraid he has stones or is in the process of producing stones. They get protein about 1-2x month. It may be overkill but I'm going to take him to the vet and have them do an X-ray to give myself peace of mind. Have you experienced this? Thanks!!!