Munroe's favorite 'What If' questions come from young children, who ask straightforward questions (like 'Can I build a billion-story building?') that lead to unexpected analytical directions, whereas adult submissions tend to be more contrived and designed to produce dramatic/catastrophic scenarios.

Astatine, in its most stable form, has a half-life of 8 hours, meaning all the energy emitted by a plutonium space probe over a century would be emitted by an equivalent lump of astatine in an afternoon.

Consulting expert chemists revealed that reality is far more horrifying and strange than Munroe's initial analysis, and this discovery process of finding that reality exceeds imagination is the most rewarding aspect of the research and writing process.

When searching for obscure research (particularly declassified Cold War documents or non-mainstream papers), appending 'PDF' to Google search terms yields higher hit rates than specialized academic databases like ResearchGate, JSTOR, or arXiv.

Mercury, depending on its form, can cause mercury poisoning which is very harmful, and beryllium, while not radioactive, is dangerous to handle and should not be touched with bare hands or allowed to contact food.

Munroe's articles frequently end with catastrophic or apocalyptic scenarios, not because he is being dramatic, but because those are the actual consequences of the hypothetical scenarios people submit, and he consults experts to verify that he is not overselling the science.

Munroe has learned to quickly skim research papers and PDFs to identify relevant material, and to rapidly discard irrelevant results, enabling him to research complex topics efficiently despite not being a domain expert.

To cradle technetium against your body for a day, eat a chunk of it, or wear it as a hat could give you a lethal dose of radiation.

Of the 118 elements in the periodic table, approximately 30 can be obtained at a local supermarket, including aluminum, oxygen, and nitrogen.

Half-life selection for nuclear power involves a balance: longer half-lives mean the element is less radioactive (decays more slowly), producing less power and heat, while shorter half-lives produce more immediate energy but decay rapidly.

Munroe has learned more about geology (continental breakup), biology, and chemistry through research for answering questions, and has found that he has historically had more difficulty with chemistry because abstract concepts like electronegativity don't connect intuitively to real-world experience compared to physics concepts like mass, speed, and force.

Element collectors typically top out around 80 to 90 elements, depending on comfort with health and safety risks, available funding, and willingness to violate international laws (particularly regarding plutonium).

In one D&D session, Munroe immediately identified a logical exploit: using a magically-enchanted weapon (heavy to others, light to him) on a water wheel, so that as it rotates and the weight alternates between heavy and light, it spins faster and faster, eventually creating a weapon of tremendous kinetic energy.

Munroe refuses to answer reasonable questions that are nonetheless emotionally unbearable, such as whether teeth could be chilled to a temperature where drinking hot coffee would cause them to shatter, because he cannot research the topic without sustained discomfort.

Building the periodic table experiment with astatine represents a 'quantity that maximizes the amount of paperwork you're going to have to face' because a smaller amount might be coverable (charred walls, radioactivity, discretely cleanable with 20% time), but a liter would demolish the building, while a larger amount would leave no one to submit paperwork.

Derek Lowe noted that burning selenium produces a smell worse than sulfur, describing it as making sulfur smell like Chanel No. 5 perfume by comparison, and that burning selenium and tellurium would be extremely unpleasant.

Munroe appreciates Google Voice transcription improvements, particularly the shift from needing to mode-switch five times to enable voice commands, to eventually being able to discretely ask voice queries like 'what's the weather' without explicit mode activation.

Munroe received concerning 'What If' submissions including one from someone with apparent nuclear weapons access asking about nuclear physics, and another from a medical doctor asking about the effects of a toxin on patient receptors at a specific dose, suggesting potential misuse scenarios.

Fluorine is the most reactive element in the periodic table, and there is a documented history of chemists being mauled or killed during fluorine experiments.

A fluorine compound exists such that almost any substance will spontaneously catch fire when placed in a fluorine atmosphere, including ice cubes in certain fluorine compounds.