She's lying on her back, legs slightly bent. Suddenly she shifts one of her legs, and I hear a soft whimper. The blankets are moving slightly. Is she... she is! I feel myself starting to flush and my pulse starts to race as I realise I've caught her playing with herself. It's incredibly embarrassing. I know I should make some noise, roll over again or something, but I can't... I'm so turned on by the thought that my sister is masturbating not three metres from me that I can't do anything but slowly slide my own hand back down, slipping a finger gently between my lips and finding my clit....