Uniquely among modern-day rugger types, Andy Farrell is learning his trade in an environment traditionally reserved for those who already know everything there is to know about the union code.
Quite what Gordon D'Arcy and Brian O'Driscoll think about this is anyone's guess, but it would be surprising if the Irish midfielders were performing cartwheels of joy. Both men served an apprenticeship and paid a few dues before laying hands on a Test shirt, only to see the former Great Britain rugby league captain flounce into the England team from the back end of beyond, garlanded by red-rose headlines every step of the way.
Hence the intrigue surrounding the game within a game at Croke Park on Saturday evening. For the first time in his jaw-droppingly short but eventful union career, Farrell will find himself up against opponents who can play a bit. For the first time in their long and distinguished partnership, D'Arcy and O'Driscoll will be taking aim at a rival whose reputation precedes his achievement by the kind of distance usually calculated by astronomers. They could, theoretically, wreck the Englishman's Test career at a stroke. It is a theory they plan to put into practice.
England know this, of course. It is why they spent a large chunk of yesterday working on a defensive system that takes into account the factors that make this weekend's Six Nations business so captivating: Farrell's strong first-up tackling, as well as his obvious lack of pace; D'Arcy's world-class footwork, along with his comparative lack of physical stature; O'Driscoll's line-cutting and offloading, combined with his... er, nothing. O'Driscoll has no weaknesses. It is why his fellow Dubliners walk the streets of the city in T-shirts declaring: "In Bod we trust."
Mike Ford, the defence strategist in the England coaching team, acknowledged the scale of the challenge facing Farrell. "Andy will have to contend with a lot of issues in Ireland," he said, after a hard session at Bath University. "That's why we've been repeating and repeating things, and then repeating them some more. O'Driscoll? His record speaks for itself. D'Arcy? He has great feet. If anything, he worries me the most. Why? Because he's such a catalyst, so central to everything they do. Between the two of them, they'll try to fix Andy as a means of getting round us, so we'll have to defend tight and avoid drifting if they get on the outside of him.
"We mustn't forget Andy has the potential to do a bit back," he added. "D'Arcy isn't the biggest centre in the world, after all."
For all that, his tone was cautious in the extreme. Another member of the cross-code fraternity, he worked with the Irish before moving to Saracens. If anyone is blessed - or damned - with a full appreciation of the threat posed by D'Arcy and O'Driscoll, it is Ford.
All things considered, it is reassuring that Farrell should feel so comfortable in his own skin. Whatever he might lack in the gas department, and however short of experience he may be after less than six months of union activity, he is not lacking in the abstractions that combine to produce a sportsman of his calibre - the strong measure of self-reliance that underpins his self-confidence, the instinctive appreciation of the possibilities offered by his chosen sport, the deep-rooted diligence that characterises his work on the training paddock and, by extension, on the field of play. Put these ingredients in the mixer, and what do you get? A professional, pure and unalloyed.
Certainly, it is difficult to imagine him dropping out of Lions Test contention with "general fatigue", as D'Arcy did in New Zealand in 2005 - an incident that provoked one wag into asking: "Does this mean he's earning more than Sergeant Knackered?" If the Irishman's burst of form has rehabilitated him in the minds of the rugby public in these islands, Farrell has still to forge a reputation of any kind. The process begins in earnest this weekend, and he understands as much.
"I want to enjoy this experience," he said yesterday. "There's a fair bit of hysteria surrounding the game, what with the recent record of the Ireland team and the whole Croke Park dimension, but why would I want to block it out? It's a part of what makes this such a fantastic event. The trick is not to allow yourself to get caught up in it. I've been around long enough to realise the importance of concentrating on the things that matter and letting everything else go by. I don't allow myself to get carried away by the hype.
"Yes, D'Arcy and O'Driscoll have something different about them, but I spent a lot of my league career coming up against Jason Robinson in training, and they don't come more different than him. This is all about taking another step along the road, a journey that doesn't stop. It's not about how good your opponents might be - we've all found ourselves up against good players before - or how big the occasion is. Those are distractions. It's about preparing properly, reiterating a few points here and there and then getting on with it.
"Will I be nervous? Yes, I'm sure I will. That's OK, though. What's bad is getting over-hyped, because that can work against you. If you put too much pressure on yourself, things tend not to come naturally during a game. People can be too serious, and they become bogged down as a result. I try to spread a little calmness, but there's always a bit of lunacy going on somewhere. To my mind, it's simple: if you've done your homework and taken the field knowing exactly what you're attempting to do, you've at least given yourself the best chance of succeeding."
Farrell's ideas are unlikely to rub off on the man occupying the position inside him - Mr Jonathan Peter Wilkinson Esq. Few players put more pressure on themselves than Jonny-boy; few are more serious about the game of rugby and its place at the centre of the universe. Yet the freshly-minted centre admires the ultra-familiar gold ingot of an outside-half as much as any sportsman he has ever encountered. As far as Farrell is concerned, Wilkinson has earned the right to do it any way he likes.
"When you go into a big game with such complete confidence in your goal-kicker, it means a hell of a lot," he said. "In the games I've played with Jonny, it hasn't crossed my mind that he might start missing." But what happens if Wilkinson does start missing? Will Farrell take possession of the tee? "To be honest with you," he replied, "I really don't know what the plan might be. I'll have a little practice when we get to Croke Park, but..." In other words, Jonny won't miss because he never misses.
We have yet to see the best of Farrell in an England shirt. Normally, this would not be a matter for concern - after all, he has played only two games for his country so far. But this is not a normal situation. The Lancastrian is on the downhill side of 30 and is not exactly unknown to the orthopaedic profession. The whole point of the Rugby Football Union spending a fortune on enticing him out of his 13-a-side comfort zone was to maximise his assets at this year's World Cup in France. In short, it is now or never.
Which is why this forthcoming collision with the most potent midfield pairing in world rugby has taken on a significance far beyond the confines of an Ireland-England match on Gaelic football territory. If Farrell survives Saturday's game with his confidence intact, the England hierarchy will be hugely relieved. If he thrives against D'Arcy and O'Driscoll, who have given sundry All Blacks and Wallabies a hurry-up in recent months, the Twickenhamites will start wondering whether it might be possible to retain the Webb Ellis Trophy after all. It means that much.