Have you ever wondered why dogs sleep the way they do. Dr. Margaret Gruen, DVM, a clinician at NC State University College of Veterinary Medicine Animal Behavior Service, says a dog's tendency to either curl up or sprawl out stems from biology and survival. Dogs naturally curl up simply to keep warm, but they also tend to exhibit a ball-like position when they feel threatened. What about the stretched out position? Well, either your dog is very hot or they're feel totally comfortable and secure in your presence. Check out these adorable photos of doggies all curled up! - By Danielle Sullivan