The line comes from the Italian dub of 50 First Dates, the 2004 romantic comedy starring Adam Sandler and Drew Barrymore, released in Italy as 50 volte il primo bacio. In the dubbed dialogue a character offers the deliberately absurd shark theory as throwaway comic advice. Italian meme pages and soundboard users clipped the few seconds of audio and shared it as a standalone joke, where its deadpan delivery made it an easy reaction to fake facts. It endures because the quote is short, quotable, and instantly silly.
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Italian 50 First Dates quote joking that sharks are like dogs and only bite private parts, used as a silly reaction to absurd animal claims.
This is the Italian-dubbed movie line where a character calmly explains that sharks are just like dogs, except they only bite when someone touches their private parts. Delivered in a flat, matter-of-fact tone, the comedy comes from how seriously the nonsense is stated, like a fake nature documentary fact. The clip runs just a few seconds and lands as a quick punchline, so listeners laugh at the confident absurdity rather than the logic. It works because the comparison starts almost reasonable, then swerves into something completely ridiculous.