Don't know, but when the stall warning sounded, the PNF said "What's that?" Another translation I saw was "What's that all about". To me, "What's that all about?" Means "What's that? I've never seen/heard of that before." Where "What's that?" could mean he couldn't quite hear the audible "Stall" or I've never seen/heard of that before. Maybe some native french speakers can shed some light on this.
Oh the idiosyncrasies of language!