If some of the leading referees in the British Isles are currently feeling a strange burning sensation somewhere in the region of the tympanic membrane – the eardrum, in layman's terms – they had better prepare themselves for a conflagration.
When the Harlequins director of rugby, Conor O'Shea, let rip at officialdom following last weekend's Premiership match at London Welsh, he did so from a position of top-of-the-table security. Now that Heineken Cup knock-out places are at stake and directors of rugby are feeling highly insecure, the language could become very ripe indeed.
Even though Quins have one meaty size 12 in the quarter-finals already, O'Shea will not be wholly comfortable with his European lot until this afternoon's business with Connacht is behind him. The English champions have had their share of fun and games with the weakest, but perhaps most cussed, of Ireland's provincial sides and while it is next to impossible to imagine them failing to qualify, they could easily land themselves with an unnecessarily difficult last-eight tie by failing to finish what they started back in October with a fine 40-point win over Biarritz.
Yet by comparison with Mark McCall of Saracens and Richard Cockerill of Leicester, the urbane O'Shea – a man very much at ease with the rugby establishment, which probably explains Twickenham's reluctance to throw the book at him for speaking out of turn – is feeling laid-back to the point of horizontalism.
Both of his fellow coaches badly need a result away from home this weekend, and if they catch the merest whiff of a referee getting it wrong at scrum and breakdown, they will be sorely tempted to "go off on one", as the jargon has it.
Ultra-wealthy Saracens play the ultra-wealthy Parisians of Racing Metro in Nantes – please, don't ask why – and if they draw a blank, they will leave themselves prey to Munster, who enjoy nothing better than picking over the bones of English carrion.
The men from Limerick are third in the table as things stand, but they will expect to take a minimum of nine points from their remaining matches and finish on 20. Should Sarries fail to take anything from their entanglement with Juan Martin Hernandez and company, 19 will be their limit.
Hence the Londoners' decision to don the full metal jacket, ready for a proper scrap against a team with ambitions, albeit vague ones, of qualifying themselves. The England midfielders, Brad Barritt and Owen Farrell, ruthless defenders both, will start today's game, as will the rough-and-ready Test lock Mouritz Botha and two highly destructive flankers in Kelly Brown and the fast-improving young breakaway Will Fraser.
As for Leicester, their trip to Ospreys tomorrow has a strong whiff of gunpowder about it. Steve Tandy, head coach of the Welsh region, has cranked things up by announcing that far from being alarmed by the raw power of the Midlanders' pack in general and their front-row resources in particular, he and his team are more than happy to engage them in a set-piece struggle.
To that end, he has picked the Welsh international props Ryan Bevington and Adam Jones in his starting formation, supplemented on the bench by another Red Dragon practitioner in Duncan Jones and an All Black tight head in Campbell Johnstone.
Leicester won the scrummaging honours when the two sides met at Welford Road three months ago and they have continued to throw their weight around ever since: not for nothing does the unusual name "Penalty Try" appear at the head of their scoring list for the season.
But the Ospreys, who have a long and rather snarly history with England's biggest club, felt they were treated harshly in that first game – yes, by the referee – and feel ready to right those wrongs.
"Leicester don't come up against a scrum like ours every week," Tandy said, "so the set-piece ain't no concern for us. We have four props who can put in a huge shift, so why should we worry about it? There's been an edge about us throughout our preparations for this game. We're in a very positive frame of mind."
All things considered, then, there is only one remaining task: to wish John Lacey, the man with the whistle tomorrow, the very best of luck.