When Willow is about to get into Buffy head (Buffy being all catatonic), she tells Anya to wish her luck. Anya's "Good luck" is obviously forced and overly cheerful in a comical way. But, as Willow is leaving the room, Anya says a quiet "Good luck" that Willow doesn't seem to hear, much like Angel does with Buffy in Season 1.
From the commentary for "Hush": I had a general notion that what it was about was the idea that when people stop talking they start communicating. That language can interfere with communication, because language limits. As soon as you say something you've eliminated ever other possibility of what you might be talking about. And we also use language to separate ourselves from other people.
I think there's something similar going on in the scenes I referenced earlier as well as in the scene where Buffy's chasing after Riley as he's flying off in the helicopter. In the two previous, the "Good luck"s aren't meant to be heard but are sincere. In the helicopter scene Buffy wants to be heard but isn't, and it's likely the first time she's been honest with Riley possibly during their whole relationship. There seems to be an addendum that communication that isn't heard can also be honest.
Which is about all I had to say and hot chocolate is ready so .... ttfn, ta ta for now.