He lay atop her,bracing himself with knees and elbows so that his full weight would not descend on her. her legs surrounded him; her thighs clamped tight against his hips; her hand slipped between their bodies, seized him, guided him into her. She began to thrust her pelvis up and down. He caught the rhythm of it shortly, and matched her thrusts with thrusts of his own.
So this is sex, he thought.
he wondered how a woman felt about having something long and hard pushed into her body like that. Evidently they enjoyed it; Lilith was gasping and trembling in what seemed like delight. But it struck him as an odd thing to covet. And was pushing yourself into a woman all that thrilling? Was this what the poetry was about, was this what men had fought duels over and renounced kingdoms for?
After awhile [sic] he said 'How will we know when it's over?'
From Tower of Glass by Robert Silverberg.