Spewage was a substance created by The Fan and The Enemy that acts as a living material that can be used to craft various creatures quickly and induct formulas and compounds into. It was primarily seen in Beorn Hallow as part of several characters' biology, although was foreshadowed in Another One. The Spewage refers to multiple things although it generally is seen as a biological god-substance.
Spewage is used to construct lifeforms; although it has only ever been explicitly used for the reconstruction of Beorns by The Fan and The Enemy, it's implied that Spewage isn't just used for this purpose and can be used to create almost kind of life. It is more noticeable with the Terran Beorns as the attempt to construct them without blood from a Beorn (such as Unten Bluzen) usually has the Spewage fight itself and become diseased and unhealthy.
Spewage is almost indistinguishable from the real thing when utilized correctly, although the blood stream of unhealthy Spewage-constructed characters often has black flecks from diseased Spewage. Spewage is most distinguished when it appears unhealthy as it will turn black and somewhat metallic in color and expose ridges. It will also expand out from the original Spewage it came from somewhat like a balloon.
The process of returning Spewage back to it's original textures, colors, and shape requires the formula to be fixed with the lifeform constructed out of it. The diseased Spewage often sags and goes limp, and feels numb and cold to those effected, as if all the nerve endings were shut off.
Spewage first appears prominently in Beorn Hallow as the substance that most of the Beorns were created from. Fenne herself is suffering from Spewage rejecting itself in her body, and only Unten Bluzen's blood was able to reverse the deadly effects. Chet almost seemed to view it in a religious sense, which he wasn't too off on in actuality. Radux sold Spewage to Unten and Litwick after believing the problem was Spewage deterioration.