When I was born, the afterbirth had a double placenta. The mid-wife (I was born at home) said something like 'oh, that's interesting' and wrapped it up in newspaper and took it away.
When I was a young child I had extra bones that poked out of my body around my collar bone. The comment from the doctor was that I had probably 'eaten' my twin in the womb and that the bones would disappear. They did!
Through out my life I have had an imaginary friend called 'Charlie' - who would announce his presence by making me feel disconnected from my body. He still appears now in my middle years - but less often and only when I am contented. It is interesting for me that I see 'Charlie' as a male - but the poem was written with the twin as female.
I have always thought of Charlie as my twin.