One-to-Many and Many-to-One

And he arrived upon the place and lodged there all night, because the sun was set; and he took from the stones of the place, and put them under his head, and lay down in that place to sleep. — Gen.28:11 And Jacob rose up early in the morning, and took the stone that he had put under his head, and set it up for a pillar, and poured oil upon the top of it. — Gen.28:18 Rashi notes that, before Jacob lies down to sleep, the verse speaks of the plurality of stones: “he took from the stones of that place, and put them under his head.” When Jacob wakes up, the verse suddenly switches from plural to singular mentioning only one stone: “and took the stone that he had put under [...]