I had s3x with my sister. My sister and I came from a messed up situation. We got new parents that took better care of us then the old ones did. I was a bought 6 years old and my sister was 8. I don’t know how we knew that the two parts fit together like that, but some how we figured it out. Once we did it the first time we started doing it a lot more. Neither one of us were able to climax so there was no real point of it. Every time we did it we knew that we needed to hide and our parents never thought anything of it. We eventually stopped for awhile. A couple years later when we were older we almost did it again. We got pretty close and it’s a good thing we didn’t because my sister fleet much would have gotten pregnant that time. We never talked about it ever again. I feel horrible that we did it and appalled that we even knew how to.