The guys coming in need to make sure they have the tempo and intensity
England coach Stuart Lancaster kept Ireland guessing by including centres Billy Twelvetrees, Brad Barritt and Manu Tuilagi in his 25-man squad for Sunday's Six Nations clash in Dublin.
Tuilagi is fit after missing England's opening 38-18 Calcutta Cup victory over Scotland at Twickenham on Saturday with an ankle injury.
In his place Twelvetrees made an assured, try-scoring debut.
Meanwhile, Barritt performed his customary role as the anchor of England's midfield defence with typical commitment.
Complicating Lancaster's task is that the last time the powerful Tuilagi played for England, he scored one and created two of their three tries in a stunning upset win over world champions New Zealand in December.
With the other positions behind the scrum seemingly settled, there appears to be no way Lancaster can, or indeed would, start all three centres against an Ireland side who opened their Six Nations with a victory away to defending champions Wales.
Lancaster is due to name his side on Friday and Mike Catt, the England skills coach, admitted he faced a tricky, if welcome, decision.
"It is always difficult but it is a great headache to have," said former England utility back Catt.
"From a team point of view you have three guys and each of them bring special attributes. It is great Billy has come along and performed the way he did against Scotland on his debut.
"Manu has been out of the game for three or four weeks. We will see how they all train and we will go accordingly from there.
"If the guys have performed exceptionally well on the weekend, the guys coming in need to make sure they have the tempo and up the intensity to really put their hands forward."
However, with Ireland likely to field a back division boasting the talent of fly-half Jonathan Sexton and Brian O'Driscoll, outstanding against Wales, Catt was not one for underplaying the importance of Barritt's defensive work.
"It would be very hard (taking him out of the equation)," Catt said.
"O'Driscoll is playing exceptionally well at the moment. I thought that first half Ireland produced (against Wales) was exceptional. We know they are capable of doing that.
"Defence is across the board. Everybody knows their roles.
"We need to focus on our attacking game too, which went pretty well against the Scots, and try and starve them of the ball so they can't do what they are good at.
"It is a little game of chess we have to try and win."
England No 8 Ben Morgan has not yet been ruled out of Sunday's match but the back-row forward, who sprained his ankle early in the second half against Scotland, was seen wearing a protective boot at the squad's hotel on Tuesday and looks increasingly unlikely to feature at Lansdowne Road.
That could lead to a return to the starting line-up for James Haskell while uncapped Wasps No 8 Billy Vunipola, younger brother of England prop Mako, is also in contention.