It could be anxiety to. Jasper does that usually to his front paws when he is upset or anxious about something. Sometimes it has gotten so bad that he get's little red sores on his legs. 1 time corresponded with a limping problem with his back leg, once when I broke my ankle, then when I had my ankle surgery. Most recently was the day we bought Hannah home from the vet and found out she was sick again. Latest incident has had Jasper after his paws for several days now. Makes me nuts and no matter what he persists unless I cover his paws with something. Our vet said we could put him on anti-anxiety meds, but unless it get's more serious or frequent I don't want to drug Jasper.