Biology homework

I’m stuck on the reproductive chapter when she walks in. Tight black lace pushes her small breasts up. A pale blonde braid swings between her shoulder blades. She drops her bag and peels off her skirt, keeping the matching panties on, then crawls across the bed until she straddles my lap. “Theory’s dull,” she says. “Watch.” Her fingers slide under the crotch of the lace and part her lips, showing me the pink inside. Two knuckles disappear, then three, and she rocks forward, riding her own hand. A quiet sound escapes her throat each time she sinks lower. When she pulls her fingers free they’re shiny. She smears the slick over the head of my cock and sinks down on it in one slow motion until her hips meet mine. She stays there, breathing, letting me feel the tight squeeze around every inch. Only when I’m fully inside does she start moving—short, rolling strokes, never leaving me, never rushing. Her braid brushes my chest each time she leans in. She keeps her bra on. The thin straps dig into her shoulders when she reaches back to grip my thighs. She doesn’t speak. She just keeps demonstrating, one measured thrust at a time, until we both understand exactly how reproduction works.