xkcd.WTF!?

Explanation ➲

Gastroenterology is the study of the normal function and diseases of the digestive system: esophagus, stomach, small intestine, colon and rectum, pancreas, gallbladder, bile ducts and liver.

Antibiotics are substances that kill bacteria. They are effective at treating bacterial infections, including in the gut; unfortunately, they can also kill the normal gut bacteria. Probiotics are harmless or helpful bacteria which are sometimes used to replace the bacteria killed by an antibiotic. This reduces chances of re-infection by pathogens, and allows the natural gut microbiome to recover more effectively; comic 1471 was about the same theme. Probiotics are included in many foods, such as yogurt, as well as supplements, and are marketed as having health benefits.

The comic plays on the names probiotic and antibiotic. When matter and antimatter are mixed, they annihilate each-other, rapidly releasing energy (an explosion). This comic imagines a similar process when probiotics and antibiotics are mixed: Ponytail and a nurse runs into a room, with someone chasing after them, leading the nurse to exclaim that “they’re right behind us.” Ponytail mixes the probiotics and antibiotics, and throws the jar like a grenade, before continuing to run with the nurse. The reaction between the probiotics and antibiotics causes the jar to explode, presumably killing the pursuer. In reality, antibiotics and probiotics are often used simultaneously during treatment, but they are taken so that they do not mix (taken at different times or by different methods). Mixing them as in the comic, would just cause the antibiotic to kill the probiotic bacteria. Explosive reactions between antibiotics and probiotics are highly unlikely.^{[citation needed]}

Matter and antimatter would react pretty much instantly upon mixing, not a short time later, as in the comic. (Also, one could not keep antimatter in a normal jar, or pour it in an atmosphere). The reaction shown is similar to the reaction between an acid and a base, or between a fuel and an oxidising agent. A judicious mix of substances (at a concentration low enough not to 'cook off' on contact) could cause an explosion after a short delay if kept in a tightly sealed container like a water bottle, or else start to build pressure that is temporarily held in check by that container, as in the explosion here. The skill of the individual constructing such a weapon would be to know how to make it effective enough without prematurely causing damage to themselves.

In the last panel, Ponytail is giving a more mundane summary of what gastroenterology is like (lots of paperwork). This is similar to Indiana Jones saying that archaeology is boring. The explosion sequence might be:

• Ponytail's action fantasy of what the job could be.
• Megan's fantasy, and Ponytail is telling her what it is actually like.
• Real, and Ponytail is covering it up.

In the title text, Ponytail adds that her work makes her aware of a child coughing as the server was bringing food at the restaurant table, exposing the food to possible germs that could cause a gastrointestinal infection.