It must have been karma that I forgot to take a picture of the rental car as I usually do.
Anyway, the rear window was "spider-webbed" and fell into a million pieces when I closed the hatchback over our luggage.
Good think the Fremont Hertz rental office was a few miles away, close enough that I could drive there, albeit quite self-consciously. The agent was very accommodating and got us fixed up with an exchange without further ado.
Two things of note:
2. That night, when I went to fill the gas tank, I thought I'd lost the gas cap. As it turns out, it's one of those cars without a gas tank cap. What a relief when I figured it out.
I think I've had enough car rental adventures to last me a lifetime.