Explicit illicit/illegal (real or fictional) drug use, addiction, and paraphernalia.
"We don't know for sure." Ed rested his chin on his metal arm, gazing unseeingly out the window. "But people go in there, and they don't come out."
One never grew entirely accustomed to having nightmares, Ed had found.
"This will feel like home, soon," Greed said when he woke the first time in this bed.