You live near me? Or, when spawning a Wither Boss in SMP, all players here an audio queue?
Everyone on the server heard it, and everyone was going “What was that?” “Oh, you heard it too?” “Sounds like someone killed the Wither.”
You didn’t see all that?
Nope, I was engaged with other pressing arrow and sword assignments 😉
But it seems when someone is challenging the Wither Boss, there is a server wide “announcement” by sound 😀