“One of the changes that [co-creator Neil Druckmann] and I felt we needed to make early on was the way the fungus would spread,” Mazin explained. “We loved the idea of biting, we thought that that was primal and violent. But we started looking at something called mycelium, which are these threads that make up fungus.” Web-like mycelium shows up several times throughout the show, perhaps most memorably when Tess (Anna Torv) gets a stringy kiss from an infected body. Sarah’s (Nico Parker) elderly neighbor and the body in Jakarta in episode two both also have some mouth-sprouting mycelia, indicating that this is perhaps one of the earliest ways Cordyceps presented.
As Mazin puts it, “these threads, if they get into an insect for instance, that’s what starts to worm its way towards the insect’s brain.” They turn people into puppets, complete with lots of gnarly-looking strings. As Gower reveals, though, the mycelia were originally intended to play an even larger part in the visual aesthetic of the show’s attack scenes. “Initially we’d created various practical tendrils, which was basically like a dental plate that we had inside the infected character’s mouth which had all these little silicone cords joined to [it],” Gower explained.
Source From: www.slashfilm.com