Gray Jelly

The Gray Jelly is a mysterious substance that develops in people with the Disease. It looks kind of like frog eggs. It is probably the Disease's offspring, or next stage in some sort of metamorphosis. It's first appearance is in The Sacrifice, when it is mentioned that grey jelly pops out of a father's head when the kids aren't looking. However, it may be referenced in The Dead, when Frederique mentions that she "does not want the red to have a baby", which supports the Offspring theory. In The Hunted, Ella finds that Malik has been collecting heads that have Gray Jelly in them. In The End, it reanimates Greg for a little bit and there is stuff that looks like half-formed bugs wriggling around in it.

The Dead
Frederique might've been referencing the Gray Jelly when she said that she doesn't want the red to have a baby.

The Sacrifice
Gray Jelly comes out of the sickos.

The Hunted
Malik collects heads filled with Gray Jelly.

The End
Gray Jelly comes out of Paul's head when Jester kills him. It also comes out of Greg. It has what looks like half-formed bugs in it.

Offspring Theory
This is the theory that the jelly is baby alien bug things, and the disease's true form. This is supported by the egg-like appearance, Frederique saying that she doesn't want the red to have a baby and the disease's alien-parasite like nature described by The Twisted Kids and Amelia Dropmore in The Hunted.

Metamorphosis Theory
This is the theory that the bug-like form of the disease is the next stage of the disease and will be used to spread it. This is supported by the disease's alien-parasite like nature described by The Twisted Kids and Amelia Dropmore in The Hunted.