My wife Terry Ann and i were drinking and got to talking about our younger years. When she and her sister were still living at home, both her parents worked swing shifts, and so they found themselves home alone overnight very often. Terry Ann discovered her father's sex video stash (this was before the internet, but after dvd porn was widely available). She began watching the vids whenever she had a chance. she discovered that her father had very wild taste in pornography. He enjoyed watching incest vids, especially ones where sisters and/or moms and daughters licked and sucked each other. 

Terry Ann found the sister encounters arousing and she would watch these and masturbate. Her younger sister, Karen secretly saw her and watched in secret. Karen was quite innocent - they were both very inexperienced, but Terry Ann was really horny over what she was seeing on the vids. Karen ended up making a noise and Terry Ann knew she was watching. Shaking, she nervously told her to come on in and watch the vids with her. Karen came and sat down as Terry Ann kept rubbing herself furiously watching the female sisters in the video lick and play with each other. 

They watched more together, and Terry Ann convinced Karen that it was ok to masturbate with her if she wanted. They were home alone that night, there was no chance of being discovered. Besides, she said to her kid sister, i think daddy actually must want us to do this. They watched all of the different lesbian vids he had, especially the incest vids. 

About 11 pm, they went upstairs to bed - Terry Ann went to Karen's room, and without much talk, she got into bed with her sister. They were both virgins and very inexperienced, but the vids had awakened a lusty hunger in them. They began touching each other and started with kissing and holding each other, their hands exploring each other's young pussies and breasts. They tried as much of the things that they saw in the vids that they could. They made each other cum several times that night, both with fingers and with licking. They had never experienced orgasm from another person before. They made love most of the night that first night and slept all night together. They got up early enough to clean up and get dressed before their parents made it home. For the next couple of years until Terry Ann moved out with me, they were more than sisters  they were lovers, taking care of each other's needs. Their parents didnt know, but their father would have been please to know that he got it going.