Why does Rachel want Leah's mandrakes? In Hebrew the word is dudaim, whose etymology might suggest a connection with dodim, "sexual love." Therefore, it has been speculated, eating mandrakes was thought to aid desire or fertility, and Rachel, barren till then, wanted them so she could conceive.
But this is not altogether clear from the text. "Mandrakes" appear in the Bible only one other time, in the Song of Solomon: "The mandrakes give off scent" (7:13). Perhaps Rachel wanted them just for their pleasant smell. That, at any rate, was the accepted idea in Christian commentary, which saw the sweet scent of the mandrakes as a symbol of a good reputation or good deeds: "the wholesome odor of a good example" (St. Gregory the Great).
In fact, the narrative in Gen. 30 is ripe for deconstruction. If Rachel wants the mandrakes to help her conceive, why does she then give away Jacob for a time? After the mandrake episode, it is Leah who conceives, not Rachel. In fact, Leah has three more children until Rachel finally gets pregnant. Gale Yee says "the mandrakes worked for Rachel" (ABD s.v. "Leah"); but did they? Rachel conceives in 30:22, after the mandrake episode is over and Leah has conceived again and again. My take is this: in a narrative that is driven from verse to verse by wordplay, there is another wordplay -- nothing more -- implicit in this pericope. Rachel may get the dudaim, but Leah gets the dodim.
There is yet one other possibility. Syrup made from mandrake root (the plant is related to the poppy) has some narcotic properties, as Shakespeare knew:
Not poppy, nor mandragora [mandrake],
Nor all the drowsy syrups of the world,
Shall ever medicine thee to that sweet sleep
Give me to drink mandragora. . . .Maybe Rachel just wanted the mandrakes to help her sleep.
That I might sleep out this great gap of time
My Antony is away.
(Antony & Cleopatra 3.5.4)
And Leah said unto her sister Rachel:
Hey, sis, I don't mean to be crude,
But you've had all this time to be lewd.
You want the blossoms?
Here! Take 'em or toss 'em!
But tonight, honey, I get the dude.