4. Whistle while you work (Season Five, Episode Six: "Buyout")
The most ominous case of TV whistling this side of The Wire's Omar and "The Farmer in the Dell." Just days after the crew's daring train robbery led to the murder of an innocent child, Walt assures Jesse – for whom the suffering of children has always been an uncrossable line – that he too is torn up about it. But then, as Jesse takes up Walt's offer of an early quitting time, Walt glibly puckers up his lips and blows – blowing away Jesse's remaining faith that Hesienberg still has a heart in the process. That jaunty little tune was nothing less than the fatal blow to the partnership at the heart of Walt's world.