Oh, I had no idea that was a real thing. (Sometimes the sources are obscure and very non-literal. In this case, I guess not...) Apparently it was in the 17th century, with rain so hard that it would wash away pets, rather than actually having them fall from the sky. Interesting.
As for "beestenweer", that may be my new favorite word in Dutch, not that I know all that many up to this point.