What amazing discovery does Hannah make about language?

In Chapter Four, a woman dressed in simple clothes asks her if he is coming. "The prophet Elijah?" she responds. "A goy zugt a vertl," says the woman. It is a phrase Hannah has heard before but now it is as if she understands it perfectly.

Hannah was stunned. It was as if she'd suddenly been transported to a movie set. The illusion was so complete, she couldn't even find an answer. And then the words the woman had spoken came to her: a goy zugt a vertl. .. . It was a Yiddish phrase her grandfather used all the time and which she'd never understood before. Yet now it was as clear as if she could speak the language herself. A goy zugt a vertl meant "As the peasant says ... "