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Explanation
This comic satirizes how the United States' stubborn adherence to traditional (imperial) units inadvertently protects national secrets.
A scene at what appears to be a formal dinner or interrogation shows someone asking a bald man (possibly a government official or spy): "How much thorium is in the nuclear warheads? Are you going to answer or are we going to kill your whole family?" The threat is deadly serious -- this is a national security interrogation.
The man responds: "One-third of a what?" His questioner clarifies: "One-third rounded or one-third of a sixty-fourth of a twentieth of a hogshead, down thirty-five yards from the fifty, give or take." The bald man responds: "Oh for God's sake."
The caption reads: "Thanks to traditional units, American secrets remain classified."
The joke is that the imperial/customary measurement system used in the United States is so convoluted and nonsensical -- with its hogsheads, yards, furlongs, and fractional subdivisions -- that even when someone reveals classified information using these units, no one (including the interrogators) can actually understand what the measurements mean. The system is so baroque that it functions as a kind of accidental encryption. This plays on the long-running joke (especially popular internationally) that American units are absurdly complicated compared to the metric system.