Cursed Womb

A Cursed Womb (呪胎) is a uterus-like cursed object capable of producing a cursed spirit.

Description
Cursed wombs that grow and change shape are expected to produce special grade cursed spirits. A cursed womb can be created from one of Sukuna's fingers. After enough time has passed, a cursed womb created with one of Sukuna's fingers can produce a special grade cursed spirit called a Finger Bearer.

In Dagon's case, he was a sentient cursed womb that resembled a cursed spirit. After being attacked and going through the emotional trauma of losing a comrade, Dagon was able to shed his cursed womb form and realize a much more powerful state of being.

Death Painting Womb
A Death Painting Womb (呪胎九相図) is a type of Cursed Womb that is half-human, half Cursed Spirit. It is unclear how they are formed precisely. In the Meiji era, the Jujutsu Sorcerer Noritoshi Kamo experimented on the nine aborted fetuses from a girl who could give birth to children who were half Curse. The first three—Choso, Eso, and Kechizu—were strong enough to become Special Grade Curses.

Trivia

 * Kusōzu (九相図) is a Buddhist series of nine paintings that depict the stages of death and decomposition of a corpse.