Witch Creek Road S4 E21 Commentary
SUMMARY: When Cassie sees the Unravelling Madness, it drives her mad; now she believes her best friend has stolen her face. And Cassie will stop at nothing to get it back...
THE EXPLOSION: Ronnie and Cassie head to the rooftop to see if they can identify the cause the explosion. The explosion, of course, was the gas station that the Serpent lit on fire in Season 4 Episode 20.
WHY DIDN'T RONNIE GO MAD? Ronnie was taking video, and was therefore looking at everything on her phone. Because she was so focused, her view of the world, and what was happening around her, was limited to what was being displayed on her phone's screen. As such, while Cassie looked directly at the Unravelling Madness, Ronnie turned the other direction and only witnessed Tenebris. When Ronnie turned to face her friend, she was focused on Cassie. By ignoring the “wider picture” of what was happening around her, she managed to avoid going insane.
SIGNAL LOST: While some people might interpret the lost signal as Cassie betraying Ronnie and killing her, whatever murderous impulses Cassie was experiencing have since left. The lost signal actually signifies something much worse - the result of which can be seen in Season 4 Episode 23.