So, I just got two gerbils. They have a four story cage with clear plastic in the front, and so far, everything seemed pretty normal. I put a sand bath in for them to bathe in, and then took it out after they were done. However, after I removed the sand bath, one of my gerbils ran to the top of the cage and started scratching like crazy at the corners. He sometimes stops and relaxes a bit, but then he runs back up and starts scratching again. Is this normal?