"His pyloric valve snapping shut indiscriminately and filling his stomach with trapped gas"

The pyloric valve (also more correctly called the pyloric sphincter) is a ring of muscle that controls the flow of liquefied food from the stomach to the duodenum. Ignatius appears to suffer from a valve that is peculiarly sensitive to stress, presumably staying open longer than it should, allowing a reflux of bile and gases from the duodenum back into the stomach and then snapping shut.

Although the pyloric valve can be affected by conditions such as peptic ulcer which would prevent it from closing properly, there seems to be no medical literature that describes a valve as wilful and hilarious as that which plagues Ignatius.