So, as of now, Pucks are gender-flipped. Male Pucks have only internal sexual equipment, while females have external sexual organs. Females penetrate males during the generative sex act. Females give birth through their external genitalia, like hyenas. When performing outspecies sex with humans - which is a possible thing in The Necklace - Pucks would be seen by humans as the opposite of the sex they actually are, and humans by Pucks likewise.
Why? For a few reasons:
Aliens are different. This concept needs emphasis. It creates interesting situations. I love interesting situations It messes completely with expectations. This is always a good thing. It brings perspective to the table. Playing a Puck gives the player a new point of view.
I will give the two players currently playing Pucks in my current game the choice of keeping their character's current sex, or changing it.