This is how both Rudyard Kipling and J.R.R Tolkien died – did you get the answer?
So, the chest X-ray shows gas under the diaphragm, which suggests a perforated ulcer. Although this X-ray isn’t from the patient described, this case did happen – a patient was suffering from increasing pain from the arthritis, and took quite a few extra ibuprofen to help with the pain.
How to prevent it? Start by reading the American College of Gastroenterology guidelines on NSAIDs and the prevention of complications here.