Dogs rubbing their bum along the floor is actually called scooting. It can happen for a number of reasons, all related to a dog having an unhappy bum! If a dog is constipated bits of poop can get stuck in the hair around its bum and the dog might scoot to get rid of this poop. Dogs have gland in their bum called anal glands and these can become blocked and cause pain, swelling or itching. Worms can also cause itchiness in a dogs bum. Scooting can relive some of this itchiness.
When dogs gets groomed it is common for the groomer to clean out the anal glands. Ewwwww! But, it keeps your dog healthy. Its also really important to give your dog worming tablets.