... plays with her pussy

With a mischievous intent, he changes the last word to pussy. The current statement reads 'Kate Smith is currently on a phone with her boyfriend Eric while she plays with her pussy.'

John immediately hears a moan coming from her room. He slowly opens a door and peeks inside. He spots her sitting in a comfy chair with her legs apart. She is naked, one hand holding a phone and a second - as you wrote - buried in her crotch playing with her vagina.

"Oh! My pussy is on fire. I wish you were here, Eric." She moans into a phone while her fingers circle around her love place.

He hears her boyfriend's voice coming from a phone but your sister's moans prevent John from understanding.

"Oh yes! It's so good." She is responding to her lover on a phone. John slowly unzips his pants and starts to stroke his dick to his sister's moans.

"Yes, right there! Oh! Yes, I'll come soon. Cum with me, my love." She continues to sex-talk with Eric but unknowingly to her brother. Her moans are faster and louder with each second and John feels he is almost done.

"I'm coming!" Kate loudly moans. Her body shivers as she experiences a powerful orgasm. John's reaction is immediate - he came in an exact moment with her. He quickly pulls up his pants and closes the door to his room. When he is about to go back to his room he hears his sister saying "Are you ready for another round, my love?"

He doesn't need approval as he comes back to the door and opens the app with a newly generated statement: 'Kate Smith is currently masturbating with her fingers deep inside her virgin pussy'. He doesn't know what's more shocking - him masturbating to his sister's sex-talk or the knowledge that she is still a virgin.