It looks like a leaking gas main!
Returns to the "Cronenberg Dimension" (Dimension C-131), where he finds his original father, Jerry Prime, living as a hardened survivor.
If you want to legally obtain the same quality as a WEB-DL, you can:
(from Season 1). Here, it is revealed that our Morty's biological grandfather is actually Rick Prime —the version of Rick who murdered C-137's family. The Wrong Jerry:
The brilliance of S06e01 lies in its decision to force the characters back to their original universes: