In this post, I will derive the sexual euphemistic phrase, "She protected the nest," or any similar variation of it.
First, it must be understood that testicles may be referred to as "eggs," as they resemble bird eggs in shape. The pubic hair surrounding the testicles may be referred to as a "bush," as its dense, stringed form resembles the object; it may also be called a "nest," as it resembles the twigs and material of a bird's nest.
Because the "eggs," or testicles, reside in the "nest," or area of pubic hair, it can be said that, "The eggs are in the nest."
The natural instinct of the parent bird is to sit on her eggs, which reside in the warmth of the nest, to incubate them. The bird may also protect the eggs in the nest from predators. Some sex positions, especially the "cowboy" sex position, involve the female moving her rear towards or onto the man's testicles. As the testicles are "eggs" and the area of pubic hair is a "nest," these sexual positions, through simile, resemble the bird sitting on the nest.