What are duda'im?

Duda'im are mentioned in the bible when Leah trades them to Rachel in exchange for a night with Yaakov.

Rachel, we're led to believe from the context, wanted the  duda'im because she thought they would help her conceive. This is the view of Rashi  and Sfrorno. Both thought duda'im were fertility-charms, similar to garlic, an herb the Sforno additionally notes, "...our Sages suggested be eaten Friday nights by men."

[Off-color aside: How many of you men in the audience think going to bed with a mouthful of garlic is good for conception?]

And what are duda'im? Various suggestions include mandrakes (Ibn Ezra,the Vulgate); jasmine (Rashi); orberries and cypress grass (Midrash). In any event this seems to be yet another case of an object's supposed properties - magical or otherwise - being connected to some pun on the item's name. Duda'im, as many have noted, is awfully close to dodim (lovemaking)

Gosh Berliner has another suggestion, writing:

'Mad honey" is made from the nectar of the toxic rhodendron flower, which grows in the Middle East. It can be lethal, but also increases blood-flow to extremities, in exactly the same manner as Viagra. For this reason, it is used in love potions and marital aids in the Near East. Can't help but thinking of the Duda'im story from Bereishit. Even though duda'im are usually translated as "mandrake," not rhodendron. 

From gizmodo 

 "Mad honey is still used as a traditional marital aide in the Middle East. A couple just recently was admitted to a local Turkish hospital complaining of chest pain. Upon examination, doctors found they also had symptoms of confusion, low blood pressure, a slowed pulse, and had both suffered mild heart attacks. The couple later admitted that they had regularly been consuming the mad honey over the course of a week—up to a tablespoon at a time—in order to add an extra bit of zing to their lovemaking"