The technical term is Ovoviviparity

No placenta in viviparous and oviparous but there is placenta in ovoviviparity

By a process called ovoviviparity. The mother keeps the eggs inside of her body until they hatch.

Their rattle, obviously, along with their venom, their solenoglyphous venom delivery system, ovoviviparity, and the fact that they are Crotaline snakes means that they have heat-sensing "pits".

Copperheads are pit vipers, and pit vipers do not lay eggs; they give birth to living young - a process called ovoviviparity.