Water Moccasins, like other pit vipers, are ovoviparous. They do produce eggs. The eggs do not have shells, but they do have a membrane to enclose the yolk and the developing young. You have probably seen a similar membrane just inside the shell of a chicken egg. The membrane is translucent, almost clear.

Sometimes the eggs hatch inside the mother, while other times, they hatch in the process of being laid, or just after.