Where the gas begins
Swallowed air and bacterial breakdown of undigested carbohydrates both contribute to digestive gas.
Source: NIDDK: Symptoms & Causes of Gas
A closer look
Follow the science page from air to digestion, then try the Fart-O-Meter. The meter is a playful interactive exhibit; its scores are invented for entertainment.
Glass, light, and a little imagination
The laboratory artwork is a conceptual illustration. Its green vapor is a visual treatment, not a claim about the appearance of digestive gas.