Ireland face arguably their biggest test of a potential title-winning RBS 6 Nations season when they tackle France in Dublin on Saturday.
Eddie OSullivans team are racing towards a first Grand Slam since 1948, having already seen off Italy, Scotland and England.
Wales will await them at the Millennium Stadium on Saturday week, when both sides could be chasing the title and championship clean sweep.
The problem for OSullivan and his players though, is that he doesnt quite know what to expect from France.
The French, awful against Scotland last month, but then brilliant for large parts of a thrilling struggle with Wales that they eventually lost, cannot secure a second successive Grand Slam, although Fabien Pelous and company can still retain the Six Nations crown.
France, there is no doubt, have the ability to beat Ireland this weekend. The big issue is a psychological one, and whether or not the mental state will be right for what could be a cracking Test match.
OSullivan, as the dust settled on Irelands victory over England a fortnight ago, openly admitted that it is virtually impossible to gauge the French mood.
If France turn up though, then Irish hopes of Six Nations success will receive a severe examination.
OSullivan has made one enforced change from the side that accounted for England, calling up experienced Ulster centre Kevin Maggs instead of an injured Shane Horgan.
Maggs will be skipper Brian ODriscolls third different midfield partner in this seasons tournament.
France, with skipper Pelous winning his 100th cap to join fellow international centurions Jason Leonard, Philippe Sella, George Gregan and David Campese, lost narrowly in Dublin two years ago.
They will be out to avenge that defeat, and no-one should be surprised if the Irish bubble is burst, but home advantage might just be enough to swing the pendulum Irelands way.
Ireland:
G Murphy (Leicester); G Dempsey (Leinster), B O'Driscoll (Leinster, capt), K Maggs (Ulster), D Hickie (Leinster); R O'Gara (Munster), P Stringer (Munster); R Corrigan (Leinster), S Byrne (Leinster), J Hayes (Munster), M O'Kelly (Leinster), P O'Connell (Munster), S Easterby (Llanelli), J O'Connor (Wasps), A Foley (Munster).
Replacements: F Sheahan (Munster), M Horan (Munster), D O'Callaghan (Munster), E Miller (Leinster), G Easterby (Leinster), D Humphreys (Ulster), G Duffy (Harlequins).
France:
Julien Laharrague (Brive); Cedric Heymans (Stade Toulousain), Yannick Jauzion (Stade Toulousain), Benoit Baby (Toulouse), Christophe Dominici (Stade Français), Yann Delaigue (Castres), Dimitri Yachvili (Biarritz); Sylvain Marconnet (Stade Francais); Sebastien Bruno (Sale), Nicolas Mas (Perpignan), Fabien Pelous (Stade Toulousain, capt), Jerome Thion (Biarritz), Serge Betsen (Biarritz), Yannick Nyanga (Beziers), Julien Bonnaire (Bourgoin).
Replacements: William Servat (Stade Toulousain), Pieter De Villiers (Stade Français), Pascal Pape (Bourgoin), Gregory Lamboley (Stade Toulousain), Pierre Mignoni (Clermont), Frederic Michalak (Stade Toulousain), David Marty (Perpignan).