Things went too fast, Cassandra just wanted to learn how to kiss from her sister and now they were making out and lieing on a comfy bed that was barely big enough for two people to cuddle on it together while sleeping. Her hands moved down to Lisa's perfect ass and began to massage it gently. Cassy was now moaning into her sisters mouth while they were kissing and spread her legs a little bit when she felt a finger entering her. She was still a virgin and never masturbated before, but her hymen got torn by climbing on trees when she was younger. There was no resistance in the way of Lisa's finger so she could go deeper or add more fingers. A warm, tingling feeling began to build up inside her body and it grew bigger with each passing second. Cassy got closer to her first orgasm thanks to getting fingered by her older sister, but then she heard a noise and looked in the direction where it came from. Their mother was standing there and looking at them, but she didn't say anything and continued kissing Lisa instead of warning her.