People also mumble when they're deliberately talking around something. For example, see this section from the audio recordings that brought down Nixon. There's

People also mumble when they're deliberately talking around something. For example, see this section from the audio recordings that brought down Nixon. There's no doubt that both parties knew exactly what they were referring to and could have expanded on it if needed. It's more clear if you listen to it: they mumble as an obfuscation tactic, likely as an ingrained habit when talking about such matters. http://watergate.info/1972/06/23/the-smoking-gun-tape.html http://watergate.info/1972/06/23/the-smoking-gun-tape.html >Haldeman: .../only way to solve this, and we’re set up beautifully to do it, ah, in that and that…the only network that paid any attention to it last night was NBC…they did a massive story on the Cuban… >Nixon: That’s right. >Haldeman: thing. >Nixon: Right. >Haldeman: That the way to handle this now is for us to have Walters call Pat Gray and just say, “Stay the hell out of this…this is ah, business here we don’t want you to go any further on it.” That’s not an unusual development,… >Nixon: Um huh. >Haldeman: …and, uh, that would take care of it. >Nixon: What about Pat Gray, ah, you mean he doesn’t want to?