When my family wasn't home, my sister's friend came to visit and it was just the two of us. While I was waiting for my sister to come home, I changed into bloomers and crawled on all fours, ``because it's more comfortable''. I got excited by the bloomers that penetrated her and when I rubbed her dick, she said, ``You can have sex with me,'' and my sister's friend, who was motivated from the beginning, came!