Sometimes it is boredom. I also read once that it could be allergies. My yellow lab does it sometimes non stop for seemingly hours.

My cat was once licking his paws then the licking increased and started chewing on his paws this lasted for 5 mins or so it was early in the morning and I was not quite ready to get up out of bed. I looked over at him and saw nothing strange at that moment. When conscious thoughts finally hit me I realized this was not normal and I went up closer to look at him. He had swallowed the feathery end of a kitty toy and most of the string that was attached to it. He was in obvious pain. I gently pulled the string and the toy worked its way out of his belly or wherever it got to.

Anyway, I would have it checked out by a vet if you do feel this concern. Nothing worse than having your suspicions or concerns amplify into something that could have been prevented.

I read last year about scotts weed and feed or most any products like that can burn your pets feet, inturn they lick and chew until they are raw. I stopped using it and this year my pets have healthy feet. Im guessing thats why. It says on the package to keep pets off the lawn for 2 days but what would scotts really care about our pets ....they want their money. Hope this helps someone. Snick :)

http://www.getipm.com/articles/letters/scottslaws-dogs.htm