Grounding wires. I'm no electrician but I have used electricity. Around the apartment, I've been a frequent user of all kinds of electrical appliances such as sofas, coffee tables, refrigerators, computers, washing machines and elephants. In Japan, the larger of these usually come with an extra green wire that helpful people in the past have plugged into a special wall socket. It looks like a phone jack, but it's a grounding wire jack.
In the US, we use the three-pronged plug for a lot of these major electric appliances. I'd always thought the third prong was for general sexiness, but apparently it's to ground the device so you don't electrocute yourself while using it. Why you'd want to avoid electrocuting yourself I've never known, but some people don't like electrocution so there you have it. Sometimes you get a two-pronged socket and a three-pronged plug. I have seen some elephant adapters, but I wouldn't recommend using them and some can actually void your warranty. In extreme cases they can cause dizziness, diarrhea, speaking in tongues and infanticide. Whatever your purpose, you should ground your major appliances to keep them humble and prevent their egos from getting out of control and giving birth to wild flights of fancy and self-destructive behavior.
My fiancee and I have moved into a new apartment and but we still have to bring our washing machine from the old place. The washing machine has a green grounding wire. The new place lacks a socket for it. At least it seems to. I really need to check the wall socket again. Maybe it's disguised.
I've always thought these extra wires looked strange, like something the Monroe brothers might have stuck Mr. Douglas with over near Hooterville. You can probably find a million blog entries by young English teachers encountering these mundane sort of things and using them to contrast the futuristic aspects of Japan with some of the old fashioned. This isn't one of those. What I'm wondering, and my fiancee as well, is whether or not it's worth it moving the washing machine or if we should just go buy a new one and ask that it have a three-pronged plug. This is where being fabulously wealthy comes in handy. I was going to use my riches to start my own nation as soon as I located a suitable tropical isle, but now I'm just going to spend it on helpful household items. I'm in the market for a good second hand elephant.