The Theoretical Physicist Always Knocks Thrice We find out in The Cooper-Nowitzki Theorem that Sheldon knows Morse code ("I'm invoking the Skynet clause of our friendship agreement."). That means the three short taps in the triple-Penny-knock could be the S of "SOS." Or possibly he's hissing like a deflated bicycle tire. Or maybe it's an "s" like in "Pssssssst!" That works. That way the knock both performs the function of getting the intended recipient's attention and also communicating information about the nature of the conversation. Okay. Maybe not. One thing we do know for sure is you don't want to ignore him. Cause he ain't going away. "knock knock knock Penny! knock knock knock Penny! knock knock knock Penny!" in white on a black 100% cotton t-shirt. And also, it's in all caps but we didn't do that here because we didn't want to look like we were yelling at you. But you should feel free to yell at people reading your t-shirt. You might notice in the action shots that there
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