Like the trigger for an Alpine avalanche, sometimes all it takes to get Broad in the mood for devastation is a single foot out of place - such as the one that failed to get Dean Elgar properly into line at the Wanderers in January last year. And when that happens, within minutes, the peace and tranquility of a pristine Test innings can be replaced, with a rumble of gathering momentum, by that dreaded sense of destiny being ripped from a batsman's hands.
At the age of 30, and with 368 wickets from 102 Tests - including a clutch of the most memorable rampages of the decade - Broad has reached the golden years of a slow-burn career. He may never earn the acclaim bestowed on Curtly Ambrose or Glenn McGrath, but no other bowler of the current era better exemplifies the merits of a genuine attack-leading seamer - the sort of metronomic tenderiser who, when he finds the spot, hits the spot. Again and again and again.
That sort of consistency may have been lacking in the early years of his career, but Broad seems in the mood to make up for lost time as he enters his absolute prime. Certainly he knows his game better than ever before, and knows how to cultivate those moments when everything feels right. Given the slightest whiff of opportunity, his ears start to prick and his knees start to pump. Every fibre of his being becomes channelled towards the top of off stump, and the edges of the bat defending it. "That brings an energy to my run-up, to make myself feel as tall as I can [and] hit the crease hard," he says.
Twice in as many seasons, that ferocious cocktail of rhythm and focus has delivered for Broad ESPNcricinfo's Test bowling accolade, and if this latest performance pales statistically compared to his 8 for 15 against Australia at Trent Bridge in 2015, then its impact was no less bone-shuddering. In the space of 31 deliveries on the third afternoon of the match, Broad returned figures of 5 for 1 - that single itself coming from a dropped catch at slip - to shatter a contest that had been resolutely in the balance for the preceding seven sessions, and deliver for England their first series win in South Africa for 11 years.
It was, in truth, the least threatening ball that Broad bowled all day, but it encapsulated the absolute dominance of England's afternoon session, and it delivered, for James Taylor under the lid at short leg, the definitive moment of a cruelly truncated career. Taylor's final Test would come one week later at Centurion, before the discovery of a chronic heart condition forced his immediate retirement, but in that short spell at the top, his work as a close catcher set new standards for bravery and alertness.
Hashim Amla could hardly have timed his leg glance more perfectly, as Broad strayed imperceptibly onto his pads, but Taylor stayed low, watched the ball off the face of the bat instead of bailing out as many others might have done, and scooped a remarkable take in the long-barrier position. It was Broad's fourth wicket in five overs, and the biggest body blow of the lot.
7 The number of times in his career that Broad had taken five wickets or more in a single bowling spell, but the first time away from home.
3 In the course of his spell, Broad went past Bob Willis's tally of 325 Test wickets to move into third place on the all-time list of England bowlers, behind James Anderson and Ian Botham.
What they said
"A perfectly poised Test match has been tipped upside down with the decorum of a wedding cake on a collapsible trestle table." - ESPNcricinfo's ball-by-ball commentary
"He just thought 'this is my time' and, jeez, he bowled well." - England captain, Alastair Cook
The closest contenders
Mehedi Hasan, 6 for 77 v England, second Test, Mirpur
Nineteen-year-old Mehedi finished with 12 in the Test, the best figures ever by a Bangladesh bowler, and gave his side a historic first-ever Test win against England.
Kagiso Rabada, 5 for 92 v Australia, first Test, Perth
Rabada stepped up after South Africa lost Dale Steyn to injury, destroying Australia in the final innings with pace, bounce, seam, swing, and searing yorkers.
Andrew Miller is UK editor of ESPNcricinfo. He tweets @miller_cricket