My 2 year old border collie/kelpie(/whippet?) cross ran into a flat rock and hurt herself. We brought her to the vet but there was nothing obvious. Three weeks later, she wants to exercise and runs at speed, but returns home with a limp. It is on and off and she doesn't respond when we check her, suggesting no major pain. I was wondering if, coincidentally, her nails might be the problem, rather than the injury.