Disclaimer: I do not own a thing. I even borrow my clothes.

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'You know Charlie, I've been thinking.' Don suddenly said, bringing Charlie out of his concentration.

The three Eppes men were all three sitting together in the living room, each busy with something or other. Charlie had been reading a thesis proposal from a student, Alan had been doing some puzzles and Don had been reading the paper. But Don's sudden comment had brought the other two men from their work.

'You did, Don? Wow.' Charlie smirked and went back to his work.

'Very funny, bro,' Don said, 'but what I meant was, I have been thinking about something specific. Math, to be exact.'

Like Don had suspected, this evoked a more permanent reaction from his little brother.

'Math, huh? You do know that's sort of my area, don't you?' Charlie asked with a smile, and pointed to the paper in front of him and the pile of books scattered around the living room.

'Well, sure... yeah. To a certain extent…' Don continued, and turned back to the paper he had been reading.

'What do you mean, to a certain extent?' Charlie asked. Now that Don had grabbed his attention, he wanted to know what was going on.

Don looked back at Charlie, and continued. 'Well, I'm not denying you're better in math than me, but…' and he stopped mid sentence again.

'But what? What are you saying, Don?' Charlie asked, unable to let this not so subtle attempt at provocation slip.

'Well… no, never mind.' Don said and he turned back to reading the paper.

'Well, now I want to know as well,' Alan joined the conversation, and he looked at both his sons.

With two persons staring at him, Don felt the urge to go on. 'Ok, I was just thinking that having lived with Charlie for so many years… I think the math has kind of rubbed off, you know?'

'What do you mean, rubbed off?' Charlie inquired, he never noticed something like that in Don before, and the thought of having been able to teach math to Don for all those years made him a little excited.

'Well, I know you were four when you could multiply 4 digit numbers in your head, and I guess I just needed 30 years to catch up.' Don simply stated, and caught the surprised look in both his father's and brother's eyes. 'For example, say eh.. 3472 times 7135 equals… eh..' Don closed his eyes, and quietly moved his lips, showing clear signs of mental calculation. After a couple of seconds he opened his eyes again and said: '24 million, 772 thousand and 720. 24772720.' With a satisfied smile he turned to Charlie.

Charlie was utterly amazed. He looked at Don, then at his father, and then at Don again and stammered, 'You're right.' He couldn't believe it. And the moment he thought that he realized that Don had to be kidding.

'But I bet you can't do it again, not when I come up with the question.' Charlie said, knowing full well how his brother might have cheated. If he had calculated the answer before bringing all this up, by scribbling it on the margins of the paper for example, Don could have easily tried to fool him.

'Ok, Charlie. That deal is on. You can come up with the question. Just give me four possible answers, and I will give you the right one. If I get it right, you get me something to drink. If I'm wrong, I will get you something to drink, ok?.' Don said. He had laid down the paper, and was facing Charlie now directly, looking him straight in the eye.

Also Alan laid down his puzzle book, for this was something he wanted to see as well.

'Well, ehm.. ok.' Charlie said. He didn't believe Don at all, and he was kind of thirsty. He closed his eyes for a second to come up with a question for Don. 'Ok, I got one. 4268 times 2375. Does that equal… 10.148.340, does that equal eh... 10.136.500, does that equal eh.. lemme see… 11.043.500, or does that equal... 11.017.300?' Charlie looked directly at Don, and could see him staring back intently.

After a couple of seconds Don answered, 'The correct answer was the second one. Am I right?'

Charlie couldn't believe it. Don had actually managed to pick the right one. 'Eh… yes. Wow. You were actually right. How... how did you do it?' Again, he looked from his dad to Don and back again.

'Well, like I said. Your math is rubbing off. At least for 4 digits multiplications it is.' Don smiled at Charlie, and then turned back to his paper like nothing had happened. 'Oh, and a beer would be great. Thanks.' Don added with a smile.

Charlie knew something had just happened, but he was a good sport when it came to bets, so slowly he got up and made his way to the kitchen.

When he was gone Alan turned to Don, whispering, 'Rubbing off? What are you talking about?'

'Well, maybe not rubbing off…, but I know my little brother for a while now. When he knows the answer, he can't help but show it on his face. You do notice that twinkle in his eyes, right?' Don whispered back, and he couldn't help but laugh.

'And I guess some years of interrogation training might have helped a bit?' Alan added, while quickly looking at the kitchen door if his youngest son was coming back or not.

'Oh yeah.' Don smirked and finally added, 'But I never thought that a genius could be so oblivious.'

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Author's Note: This title and story was inspired by the story of Kluger Hans (or in English: Clever Hans).