Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic contrasts "Good Science Teaching" with "Fun Science Teaching." In the top panel, labeled "Good Science Teaching," a teacher tells a student: "Every time you take a breath, you're breathing a few atoms that were once in Elvis' lungs." This is a real and fascinating scientific fact -- because atoms are recycled through the atmosphere over time, and there are so many atoms in each breath, it's statistically likely that any given breath contains atoms that once passed through the lungs of any specific historical person.

In the bottom panel, labeled "Fun Science Teaching," the same teacher applies the same principle but in a crude direction: "Every time you drink water? Couple atoms of Charlemagne's balls." The joke is that the same atomic recycling principle that makes for an inspiring science lesson can also be used to produce a hilariously disgusting observation. The scientific reasoning is equally valid in both cases, but the second version sacrifices educational gravitas for shock humor.

The votey extends the gag with a "Math Challenge: What are the odds an atom in a cup of water has an atom that was in Charlemagne AND Napoleon's balls?" This turns the crude joke into a legitimate combinatorics problem, blending lowbrow humor with genuine mathematical thinking in a way that is quintessentially SMBC.