The spatter of matter.
The new theory, supported by some radio and X-ray astronomy that even I can sort of grasp, is that black holes spit out quite a bit of energy in the form of twin jets from their poles. This is easier for me to understand than just the Hawking radiation that we first were hearing about in the late 1980's and early '90's.
It makes the superdense things seem less of a curiosity, to me. We always wondered where matter might go. I know. It's foolish to think such things.
But it brings to my mind that old question about recycled mass. I've heard various speculations about how, given the way that water evaporates and then gets redistributed, we all have likely molecules of water in us that ran down Jesus Christ's (or Herod's, or Moses, or David's, or Muhammad's) throat. What of interstellar matter that gets split off and spat out by a black hole, only to feed a nearby galaxy, then be pulled into the ever-growing black hole? Surely there's a chance that some of that matter will be recycled and spat out again. Some even again.