Leading up to the conclusion of “Death of the Family,” the Joker has been kidnapping Batman’s sidekicks. At the end of each bat book, he teases to unveil a bloody silver platter.
“Since your hands will be tied, I’ll be the only one allowed to carve the meat,” Joker tells them. “For your sake, I do so hope the knives have been sharpened.”
The implication is that they’re the meat. It’s noteworthy that each time we see through the abductee’s eyes, which suggests the whole Bat-Family will lose face in Batman #17.