Dean swung a tire iron, the metal clanging against her skull, but she didn't drop. It took three more hits to ground her. He stood over her, chest heaving. "These aren't demons, Sammy. They’re 'Rabids.'"
If you want to explore more about this specific era of the show: The psychological bond between Sam’s secret struggle with the Rabid infection Castiel’s torture at the hands of the angels [S11E1] Out of the Darkness, Into the Fire
They climbed back into the car, the rumble of the engine the only familiar thing left in a world that had suddenly turned alien. As they drove toward the nearest town, Superior, Nebraska, the signs of the "Darkness" began to manifest. It wasn't monsters in the shadows; it was a sickness. Dean swung a tire iron, the metal clanging
Tell me which character's perspective you'd like to dive into next. "These aren't demons, Sammy
"It’s a localized infection," Sam whispered, hopping out of the car to inspect a fallen road worker. "Whatever that smoke was, it changed them."
The first body they found was slumped against a road sign. Then another near a rusted-out truck. These weren't demonic kills or angel smitings. The victims were covered in black, veiny growths, their eyes wide and vacant, as if their very souls had been vacuumed out.