The rule he gets right has to do with the apostrophe when you want to make a word possessive.
If the word you want to make possessive ends in “s,” just add an apostrophe; don’t add another “s.”
But you pronounce the possessive as if that second “s” were there! So it sounds like “Joneses.”
A head locker room attendant is a janitor, right?
This post first appeared on The Writing Rag.