Friends after school

Mummy thinks I'm studying algebra with my best friend. Instead we're on my bedroom floor. She works three fingers in me, then four. My knees slide apart on the carpet. A knuckle catches. She keeps her thumb folded and pushes harder. My cunt gives. We hear it, wet and low. Her wrist twists. My walls clamp. I tilt my hips, feel her knuckles turning inside. The stretch burns then melts. When she opens her fist, the pleasure jumps up my spine and I bite the inside of my lip to keep quiet. Later she lets me practice. I coat my hand in her slick, tuck my thumb, and watch my own fingers disappear. Her pulse flutters against my palm. A small sound escapes her when I make room for more.