xkcd.WTF!?

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LD50

The dose is much lower when administered orally. We're still trying to get the paper into the needles for subcutaneous injection.

Explanation

LD50 is a term used in toxicology that identifies the median lethal dose of a toxin, or how much is required to kill 50% of a given population. LD50s are usually measured in g/kg, as the amount of toxin to kill something is usually linearly related to its mass. The lower the LD50, the more lethal the toxin. An LD50 can be determined for almost any substance: for example, the LD50 for sugar (in rats) is 29.7 g/kg. However, Botulinum toxin (commercially known as Botox in the beauty industry), the most acutely toxic substance known, has a LD50 of roughly 1 ng/kg, or 0.000000001 g/kg, a vanishingly small amount.

The comic is making the joke that the LD50 of papers on toxicology is 2 kg/kg, so it takes 2 kilograms of papers on toxicology to kill a person for each kilogram they weigh. The worldwide average weight of an adult is 62 kg (137 lb), so the lethal dose would be 124 kg (273 lb) of toxicology papers. Death is apparently caused by compression or smothering, rather than any form of toxicity.

The title text says it will take less paper to kill a person if the paper is shoved down their throat instead of dropped on them, either by suffocation or bursting the subject's stomach. A third method of delivering a toxin is by subcutaneous injections which are highly effective in administering vaccines and medications, but that number is omitted since they couldn't figure out how to do it. The amount of paper required to trigger a fatal blood vessel blockage would probably be fairly small if they could.