Racing stripes would be a better example. Though negligible, a hand out the window does have a causal impact on speed.
On the other hand racing stripes have zero impact, but do correlate to the speed of the car.
We could pick a company car in my previous company (it's a tax thing). We could pick any color, apart from red, because the insurance forbade it - red cars get into more accidents. Somehow that must have made it all the way to the policy without someone asking "is it the red car or the kind of person that picks a red car that causes more accidents?"
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What about speed holes?