Scripture says that Jacob's family went down to Egypt numbering seventy souls (Genesis 46:27). When the sages sat down to count the names listed in the chapter, they reached only sixty-nine. One soul was missing. Who was the seventieth?
Rav Cheyah proposed an answer based on a small grammatical particle in verse 15. That particle, he said, implies that Dinah was actually one of a pair of twin sisters, and her unnamed twin made up the seventieth soul.
A colleague pushed back. "The same particle appears in the passage about Benjamin," he said, "and in other places besides. You cannot build a twin on a particle that behaves this way everywhere."
Rav Cheyah sighed. "Alas, I am guarding a secret worth knowing, and you are trying to extract it from me." He would not say more.
Then Rav Chama bar Chanena stepped in with a cleaner solution. "The number is made whole by counting Jochebed. Scripture says of her that 'her mother bore her to Levi in Egypt' (Numbers 26:59). She was conceived on the journey but born at the moment of arrival, between the wall and the gate. She is the seventieth soul, the first Israelite born on Egyptian soil, and already the mother of the redeemer to come."
The missing soul turned out to be the one whose womb would one day hold Moses.