‘And she said to her, “Is it a small matter that you have taken away my husband? And would you take away my son's mandrakes also?” And Rachel said, “He will therefore lie with you tonight for your son's mandrakes.”
Leah feels cast aside. Perhaps Jacob has decided she is beyond bearing. Certainly he seemingly refuses to sleep with her, preferring Rachel. So Rachel, aware of her power over him enters into a contract that if she receives the mandrakes Leah can sleep with Jacob that night. Indeed the next verse suggests that the contract may well have been in accordance with tribal custom between two wives.