VW Beetle Tire Blowout
RAY: Helmut guessed they needed a tire repaired based on the fact that the windshield washer in the Volkswagen of that era operated on the tire pressure of the spare tire.
If the tire pressure dropped down enough, the washer would stop working, and save enough air in the spare so you could use it as such. But if you had a flat and you had no air whatsoever, then you would have no windshield washer. And thus a mud splattered windshield.
[ Car Talk Puzzler ]