
I have a Bearded Collie who does this on a regular basis, bless her. She is always sedated, and I do give her metacam after 24 hours, and she gets it daily if needed for 3 or 4 days. The "shell like" covering does take a while to build up and give protection, as the nerve endings are exposed after. If a Chihuahua stands on her foot, or knocks her accidentally, she really cries out. I did ask my vet if she was just being a baby. She is a huge dog. He said no, it really hurts like hell.
If a Chihuahua can get a response from old droopy drawers, I'm guessing that Fred won't want to be knocked by an unknown dog. Just my thought on it, but I do deal with this scenario regularly with Cassie.