Our hearing is more sensitive than we give it credit for being.

We used to play a game in my dojo where we'd toss a "knife" (wooden) around in a circle, as if sending it to an ally. Yes, you could throw it in a way that can't be caught... but then the person picks it up and chooses how to throw it back. You learn quickly not to be a dick about it.

Naturally, we were trying to get better at catching, and eventually moved to a trust version, where I shout "Go!" as I throw the knife. Turns out you can hear the knife leaving someone's hands more reliably than they can shout "Go!" on time.