well… not all cats are female, otherwise they would be extinct by now. The male version is called “Kater”, wich in German also means hangover. For whatever reason :) So, the “ein” is correct, the “Katze” doesn’t fit. And fitting the accent only would make the Katze “ein Berliner”. RIP JFK.
I thought they were mice. And they used us as a huge calculator. But, on the other hand, and related to the OP, Bill Watterson himself is quoted with these words: “The surest sign that intelligent life exists elsewhere in the universe is that it has never tried to contact us.” I completely agree.
it would also convey a lot of other information to the culturaly interested species sniffing at the art piece.