In actuality, it's a joke.
I wanted to make this due to the fact it bugged me in the movie that Jake managed to nail Neytiri with little to no knowledge of Na'vi mating practices. I mean, I'm assuming it's pretty similar, but considering they have magic hair veins that connect with nature, there's obviously some pretty big anatomical differences...
Ex. Where Jake's snake would be is a giant straw ("soupdrinker"), Where Neytiri's vagina would be she's able to play a flute ("second pair of lips"), they have to connect their hair to exchange fluids, etc.
Curiosity kills the cat.