Even though I have literally seen thousands of births, it still amazes me.
The woman is pushing and at first, just a smidgen of head is visible if I'm separating the labia. Then after some more pushing, the head is seen without my assistance (at this point, I'm frequently styling the hair into a ponytail/mohawk). Then a few more pushes, and she's crowning.
And then it's done. Once the baby crowns, it's pretty quick. But it's so cool to see the head come out, turn, and then the rest of the body follows.