Is the word screw came from the study on duck sex? Read this article from Discover Magazine.
“In brief, Brennan wanted to understand why some ducks have such extravagant penises. Why are they cork-screw shaped? Why do they get so ridiculously long–some cases as long as the duck’s entire body? As Brennan dissected duck penises, she began to wonder what the female sexual anatomy looked like. If you have a car like this, she said, what kind of garage do you park it in?
Brennan discovered that female ducks have equally weird reproductive tracts (called oviducts). In many species, they are ornamented with lots of outpockets. And like duck penises, duck oviducts are corkscrew-shaped. But while male duck penises twist clockwise, the female oviduct twists counterclockwise.
Brennan speculated that all this bizarre anatomy is the result of a peculiar form of evolution known as sexual conflict. A strategy that allows females to reproduce the most offspring may not be so good for males, and vice versa. For example, male fruit flies inject their mates with lots of chemicals during sex, and those chemicals make her less receptive to other males, thereby boosting his chances of fathering her eggs. But those chemicals are harsh and will make female flies sick. Females, in turn, have evolved defenses against those chemicals, blunting their effects.”