How are wires placed inside extending single-wire headphones?
Even though this has been downvoted a bit, I still think it is a good question because there is a lot of ingenuity in these designs. I have disassembled a fair few of these types of headphones and I can say that there is no single solution.

By far the most often used way is just a bent flat flex - very wide, and very thin. My Logitech H800 uses this technique. Apparently, it is acceptable to have about 2mm-radius bends in this material, probably provided you use very thin copper to avoid cracking.

Another option that I have seen used in my Sennheiser is to have a long serpentine flat flex going all around from one ear to the other. This seems to me like total overkill, and because of the limited available copper I suspect this is only possible with very low current signals (like just driving a headphone coil). This would not be possible in the Logitech example, because that device also carries battery/charging power over the flat flex.

Lastly, in a very cheap headset I have seen just sliding contacts being used. I suspect this to be very low endurance, as exemplified by the short lifetime of that headset.