In Toph's car, on his wiper stalk, there is the rotaty knob thing as shown in the image below by the big arrow.
The question I put to you is... "What does it do?" Now, we guess it's something to do with the auto rain detection wipers... but we're not sure as turning it doesn't seem to do much to the action of detecting rain.
RTFM, I can hear you cry. We did... it doesn't say!
If you would like to read the relevant section of the manual yourself, to aid you in your quest for the truth, click on the image and it'll open big and readable, like.
The car is a Nissan Micra, if that helps.