could it maybe be possible that one of them sustained an injury of some sort and the sands stuck to it?
or maybe the 2 of them had a fight and thats why they both have sand stuck to them?
well we only have the one now and it was just that once. and yes he is on sand substrate...... he also just shed his tail.... and looks beautiful.... im just wondering is it normal when they are shedding to dig in the sand and hide..... he does not cover himself with the sand. he just makes a lil hole so that he can lay in it