2018 Six Nations: Ireland's Grand Slam bid hinges on defence
Ireland's defensive problems have been a recurring theme in the 2018 Six Nations and it is their biggest concern as they target an elusive Grand Slam.
After conceding three tries against both Italy and Wales, Joe Schmidt was moved to back his defence coach Andy Farrell, calling him "world class".
Ireland responded by allowing just one try against Scotland but their resolve will be tested again at Twickenham.
Against England, Farrell faces his toughest opponent yet - his son Owen.
Whether Farrell junior starts at fly-half or at inside centre for England on Saturday, he will know how best to unlock a defensive system that has threatened to collapse on several occasions in this year's championship.
Andy Farrell was left "fuming" by the failure of his system earlier in the competition, reminding players that "average is not acceptable in this environment" after Italy scored three tries against them in the final 25 minutes.
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"He's got the confidence of our group because they can see the system works," said Schmidt of his defence coach after outscoring Wales by five tries to three.
"Andy's doing a great job, not just with the team, but with individuals. Trying to get them to understand the pictures, so they make good decisions."
Scotland managed just a single try in Dublin but Gregor Townsend's side should have scored more as they cut open the Irish defence numerous times, making eight clean line-breaks and beating 18 defenders for 420 metres.
Schmidt and Farrell senior will know that the 'one try conceded' statistic masks a lingering concern about Ireland's vulnerability on the fringes of their defensive line.
The positioning of the likes of Jacob Stockdale, Dan Leavy and Bundee Aki have all been questioned during this year's championship but the dressing room remains committed to Farrell's system.
"There was probably a lot of talk outside of the camp about our defence and what we can do," said flanker CJ Stander after the Scotland victory.
"I think Andy Farrell gives us all the tools during the week and we just need to go out there and perform for him - he's a very passionate man."
"Those were small, individual errors we had in the first few games," added Stander.
"I think a few players stepped up and we got into that space and just put their skill set under pressure and those passes didn't come off but if they had they probably would have scored tries."