DC Universe's Swamp Thing has introduced the force known as The Rot into the series' mythology. While not identified by name in "He Speaks", The Rot is mentioned in the episode 3 summary on the DC Universe website.
Swamp Thing episode 3 opens with a dream sequence in which Alec Holland, the man who became Swamp Thing, is confronted by Munson - a hired thug in the employ of industrialist Avery Sunderland, whom Swamp Thing had killed in the previous episode. While Holland is apologetic, Munson is enraged by Holland's sympathy and declares that he is going to come back and kill him. We then see Munson's corpse in the swamp being surrounded by flies and cockroaches, as his hand begins to twitch. While the precise meaning of this was lost to some viewers, longtime fans of the Swamp Thing comics will instantly recognize this as a reference to The Rot, which animated corpses into zombies with swarms of vermin.
The Rot is a relatively new entry into the mythology of the DC Comics universe. First appearing in Animal Man #1 in November of 2011 as part of the New 52 revival, The Rot is a force associated with decay and death, which seeks to destroy all life. The Rot stands opposed to The Red, which connects all the animal life on Earth together, and The Green, which does the same for plant life. In the comic run, the hero Animal Man calls upon the power of The Red to replicate the abilities of animals, much as Swamp Thing draws upon The Green to control the fauna around him and transform his body to take on aspects of particular plants. The two heroes joined together to fight an uprising in The Rot in a crossover event called Rotworld.
The latter half of "He Speaks" sees Swamp Thing saving Dr. Abby Arcane from Munson when the zombie threatens her while she is exploring Alec Holland's lab. After knocking Munson to the ground, Swamp Thing seems to recall his dream vision and, rather than destroying Munson, merely tells something within the corpse to "release him." For some reason, the animating force complies, and Munson's body dissolves into a pile of loathsome insects. With the threat passed, Abby has her first chance to speak to the creature that has saved her life twice and confirm that he was Dr. Alec Holland.
It is hard to say just how The Rot may manifest in future episodes of Swamp Thing or how it may already be connected to the strange properties of the swamps surrounding Marais, Louisiana. It might have something to do with the dreams Maria Sunderland continues to have about her deceased daughter, Shawna. It could also be connected to the degenerative brain disease infecting Dr. Jason Woodrue's wife, Caroline, which is pushing his research into the swamp. The only thing that seems certain is that while it may remain hidden for now, The Rot will make itself known again.