Hedgie nails begin to curl and push into their feet when they have grown too long. It happens with hedgies, guinea pigs, birds, etc... The important thing to do when you see it happening is to trim the nails immediately and then make a point of trimming your hedgie's nails more frequently; ie, before they begin to curl under. Once they begin to curl, it can become painful for your little one to walk. And then, once they grow long enough, they will puncture your hedgie's soft little feet. At that point, you'll likely need to call in a veterinarian for assistance.