Brandy had a limp for a while. She was holding up the rear foot when she ran or walked. We would poke and feel all around it and could never get her to yelp. It was when she was pretty little and got stepped on a lot (not totally stepped on but enough to cause the occasional yelp
) After a few days I took her in for x-rays and found nothing. My vet had a specialist look at them and he couldn't see anything wrong either. Brandy continued to limp and favor that leg for several weeks until one day we finally realized that she had stopped limping. It may just go away and you may never know what it was.