satan-fingers
Explanation
The Joke
A father catches his son and asks, "Son! Have you been touching yourself?" -- a setup that sounds like the beginning of an awkward puberty talk. But instead, the father warns that the boy will get "the Satan-Fingers" -- hands that get evil powers. The father then demonstrates a well-known multiplication trick for the 9 times table: to find 9 times 5, hold up your fifth finger and count the fingers on either side. The child sees 4 fingers on one side and 5 on the other: forty-five! The father dramatically declares these are "Satan-Fingers!"
The child nervously suggests it might be a coincidence. The father then asks what 9 times 9 is and tells the child to hold up his ninth finger. The child sees 8 and 1: eighty-one. The father triumphantly declares the child has the Satan-Fingers and demands he confess his sins. The terrified child starts confessing: "I did it! I did it! I am garbage! Garbage!" At the end, the father (now shown in sinister silhouette) breaks character and explains that it is actually just "an interesting property of nines" and that the child will never forget it. He adds, "I hate you" -- presumably the child speaking.
The Humor
The comedy comes from the father using elaborate psychological terror as a teaching technique. Rather than simply showing his child a neat math trick, he frames it as demonic possession, scaring the child into an existential crisis before casually explaining it is just arithmetic. The father''s smug satisfaction in the final panel -- noting that the child will "never forget" -- reveals his twisted pedagogical logic: traumatic learning experiences are, technically, very effective at creating lasting memories.
The initial misdirect about "touching yourself" sets up the expectation of one type of uncomfortable father-son conversation, only to deliver an entirely different (and arguably worse) one. The child''s overwrought confession -- "I am garbage! Garbage!" -- in response to a math trick is a darkly funny escalation.
References
The "nines trick" is a real and well-known method for multiplying by 9 using your fingers. To multiply 9 by any number N (1-10), hold up your Nth finger; the fingers to the left give the tens digit and the fingers to the right give the ones digit. This works because of the mathematical property that in any product of 9, the digits always sum to 9 (e.g., 9x5=45, 4+5=9). This is a consequence of 9 being one less than the base of our number system (10).