Board Thread:General Discussion/@comment-24589671-20150309010651/@comment-25355646-20150312003954

Zelena didn't use Regina's blood to recreate the curse. I figured Zelena was just using the blood to make sure she Regina's sister (A&E confirmed this at some point). And Regina was able to help Snow with preparing the curse without the scroll because we see her absorbing the scroll into her hands in 3x11. Regina was able to split the heart in half because there was enough light magic in her heart since Snow was awaken from the sleeping curse so that her heart could keep both herself and David alive. Snow said: "We have been of one heart since the day he woke me from the sleeping curse."