My favourite example came from my 9th grade physics class, our textbook told a story that attempted to teach scientific method. Imagine a soda vending machine. Now imagine that I tell you that when you insert money and press the buttons, small goblins are can see what buttons are being pressed, take the money and it put it in a box, and then hand you the selected soda. The textbook even had helpful diagrams that seemed plausible (presuming you had such creatures). Now tell me why this is or isn't so ... and prove it even! How many of you have ever opened up or observed a vending machine (well, on HN I bet that number is surpassingly high, but presume you haven't). It was fantastic exercise in intellectual humility.

For your SD Card example though, I'll nitpick. Sure, just a card and explanation won't get you very far ... but I think something like an iPad (with a good power-supply) would produce enough evidence to convince them (depending upon the individual, I grant there might be some who just attributed it to supernatural forces even in the face evidence and explanation). I suspect humans in general are more willing to deal with "blackbox" technology that has practical application than most tinker types on HN would admit. Very little historical technology that was hard earned with trail-and-error has a theoretical basis known to even skilled practitioners. Even today, to most most people I know, the technology they use on a daily might as well be magic. Sure they know there some kind of "science" beyond it, but I'm also not sure they could convince me it wasn't just goblins if I demanded some theory of it worked.