So i was having intercourse, and without going in to much detail, my semen ended up in a mouth and the reaction was unexpected, because my partner felt something that wasn't supposed to come out of me so she caught it with her front tooth and tried to bite it of, but the material was tough and it didnt work so she pulled it out and I felt it on the way out, so it wasn't, like.. There before, and then I took it from her cleaned it and looked at it, it was similar to a fishing line. And I just want some answer's here, how could it have ended up there? 

It also had a knot on it..