Today I would like to talk about twins. Most twins are in separate sacs. It is rare, but sometimes both twins can be in just one sac but usually, they are in separate ones. One twin will be called baby A and the other twin will be called baby B. The reason they are labeled this way is that, during vaginal birth, the baby in the sac that includes the cervix will be born first. This baby is called baby A. The baby born afterward is logically labeled baby B. While the twins are developing in the womb, the membrane separating the twins is not stiff. A lot of people want to think that the separation between twins is like a wall. It is actually more like a bedsheet hanging on a clothesline. The babies can nudge each other and kick each other. But they cannot directly touch each other because of the flimsy membrane. This membrane is very strong, though, and they cannot tear it. They can, however, punch, and kick each other through it. I frequently see babies in the womb doing this. It is hilarious how much they play with each other.