This thin cable is actually endoscope.It has camera on one end,and micro usb plug on the other:
You can take photos,videos and even sound,and it's waterproof.I think it's most useful for inspecting water pipes.Just stick the wire in pipe and see where is the problem.Obviously it's good for taking videos of any hard to get place.
It works on Android mobile phones and computers.
It's available in different cable sizes,and it's relatively cheap.
Best price that i could find for 5M cable is around 10 USD on ebay.
If you want link to ebay,ask in comments below.
Source of images: ebay
Please subscribe for more cool gadgets! :)