בראשית, פרק ל׳, פסוק י״ב

The birth of Jacob's second son from Leah's maidservant, Zilpah, happens with unusual suddenness. The customary stages of conception and carrying the child are completely absent from the story, moving directly to the moment of birth. This omission reflects a physical reality: Zilpah was extremely young, and her pregnancy was entirely unnoticeable. Her physical changes were so slight that even she did not realize she was expecting a child [צאינה וראינה בשם רש״י].

This detail about Zilpah's young age also sheds light on a much earlier event, revealing the depth of Laban's deception on Jacob's wedding night. Laban deliberately assigned his youngest maidservant to his oldest daughter, Leah, in order to create a convincing illusion. He anticipated that when Jacob noticed the young maidservant in the room, he would naturally assume the bride in the bed was the younger sister, Rachel. It was a calculated move, relying entirely on the expectation that the youngest maidservant would accompany the youngest daughter [צאינה וראינה].