I just went to feed my rats and play with them for a little bit (I have 4) and I noticed that my largest rat, Aberdeen, seems to be limping. She's not using her back right foot when she walks but I don't see any cuts or anything on it or on her leg. Is there anything I can do to help her? I just noticed the limping today but she wasn't very social when I went to get them out yesterday. She still seems to be eating and drinking.