Misty is just one of an untold number of customers in a relatively new, but growing market — pot for pets. These aren’t the edibles or oils that contain THC — tetrahydrocannabinol, the psychoactive compound in marijuana that provides the “high” in humans — although there are some products being sold that contain low doses of THC. These are hemp-based products that provide relief for all sorts of doggie ailments, from arthritis to cancer to anxiety.And in an industry where pet owners spend an estimated $72 billion a year in the United States on supplies, veterinarian bills and medications, according to the American Pet Products Association, some experts believe the next big thing for doting dog owners is cannabis.