Fool proofing in design (Pokayoke in design)

I love computers and technology. Not only because they are very close to me, but because I find them interesting. I like designs of computers and their usability. I always quote computers as very fool proofed designs. We can not plug one cable in some other socket. But I doubt this is applicable to every computer peripheral, at least I found a thumb drive which is exception for the rule

Compare two thumb drives (data travelers) on the image. What is the fool proofed design?

What do you want to keep with you? Is that the clip or the data storage part of the thumb drive?