Also, if you use undead rapport on mobs without helmets/visors, their eyes change color so you can tell which ones are under your control, and how long the spell lasts.
Finally, if you are gravelorded, all the gravelord BPs respawn if you quit and reload, even though all the regular mobs stay dead and you never touched a bonfire. They also respawn if you are summoned and then return back to your own world. The latter is particularly nasty if you were summoned out of an area you had already cleared, and didn't expect to be surrounded by BPs when you eventually made it back to your world.