Fetuses, also referred to as Babies, are objects that only appear in the Flesh Tunnels. The sound of their bouncing can be heard in the winding halls of the tunnel. Players can often find a lone one somewhere in the hallway, which will quickly leap in the other direction and disappear through a wall. Taking a short detour around this wall will lead the player to a large room filled with multiple fetuses bouncing in place and spinning in the air. Touching them will link you to Monument Park.
The kanji that appears on their stomachs 胎 reads "Fetus" or "Womb".
The Flesh Tunnels are generally thought to represent the inside of the human body, as suggested by the name, inner design, and the fetuses. The red aprons they wear cause them to resemble the Japanese folk hero Kintaro, which was likely intentional.