that's what I thought. I don't even recall ever reading anywhere that they burrow (not even on the comprehensive mandarin primer thread). so one morning I found my mandarin covered with sand (the sandbed has a small lump in the shape of the mandarin, so I assumed it was the mandarin). so I thought, man, my mandarin died, so I was about to scoop it out and it started swimming around. since then I see it buried under some sand (I don't have a deep sandbed, maybe only half inch or less in some areas) at night when I check the tank.