As I was testing an issue with the credits music (please see issue 40275), I happened to stray idly by a witch. Since I had the development console open next to me, I immediately saw an error which said:
"Unable to play unknown soundEvent: minecraft:mob.witch.idle"
I tried hitting the witch, and not only did I hear no sound, but I also got:
"Unable to play unknown soundEvent: minecraft:mob.witch.hurt"
Upon examination of the /assets/minecraft/sounds/mob folder, I discovered that there was no directory for witch sounds! How did that happen?
There are no witch sounds, but their paths are coded into the game. The same thing happens with "step.anvil"