The Binding of Isaac Wiki

A cluster of red cellular flesh.


Makes a fetus grow on the side of Isaac's head.

Increases available maximum Heart Containers by one and heals one and a half-hearts.

In original Binding of Isaac, it also increases Shot Speed by 16%. However this effect is removed since Rebirth.


  • Stem cells are an undifferentiated cell of a multicellular organism that is capable of giving rise to indefinitely more cells of the same type, thus why another human is growing out of Isaac.