A couple of signs that you may have a rodent problem. This kind of burrow is very common in homes with a stone foundation. This happens to be from rats, but mice burrowing looks very similar. Mice and rats use the stone foundation as the perfect home. They easily can make a home within and remain fairly well protected. Foundations like these let in more than mice or rats. They also allow entry for insects, snakes and moisture. Parging or cementing the walls is going to give you a barrier from these pests.