Jason, does Scamp have a history of geriatric osteoarthritis - difficulty rising from a prone position and/or jumping up or down? Was today's walk longer or more strenuous than Scamp's usual walk? It would reasonable to see how aspirin dosed at 20 mg/kg with food every 12 hours affects Scamp. Paracetimol dosed at 15 mg/kg thrice daily is OK but it isn't antiinflammatory as is aspirin. You must avoid the toxic ibuprofen and naproxen.