Interestingly the article about steganography does not mention the term even once.

Relativity would prevent this. If the train moves at the speed of light, then nothing inside it will move because time will stop. The amount of trains inside trains doesn’t really change much except the effect of time dilation (slowdown) on each train. You can’t actually accelerate to the speed of light.

While light bulb sockets don’t change much from region to region, they definitely aren’t all the same. For the bulbs (not the bars), there’s two large categories: Edison screws and bi-pin. Edison screws also come in a lot of sizes. When compact fluorescents were rolling out, they got a new bi-pin connector from the USA: GU24. My whole home has GU24 fixtures (not by my own choice), but my lamps are Edison screws.