The car runs, the cars run; the cast travels, the cast members travel. One of the silly copyeditors who write blogs (not one of the housewives who reads McCall's--which was the ad campaign while I worked there; and of course, nobody realizes that the magazine's copyeditor doesn't get to sign off on the circulation department's ad agency's copy).
I can do subject-verb agreement; that's Grammar 101.
But there's an agreement that I find myself missing on first read.
Vases of flowers served as centerpieces on each table.
Each table does not have more than one centerpiece.
We start w/ vases, which become centerpieces. Excellent, two or more vases = two or more centerpieces.
But then, we need two or more tables upon which to place those centerpieces.