Analysis: Scotland have power at loose-head to cause Irish scrum problems
Much like Ireland, Scotland have an imbalance of wealth at the scrum.
While they have plenty to offer at loose-head - with Ryan Grant stepping in for Alasdair Dickinson this weekend - they're vulnerable at tight-head, with Euan Murray no longer as able as he once was to dominate the set-piece.
Dickinson can count himself unlucky to be starting on the bench this Saturday, but Grant's physicality and technique gave Mike Ross some trouble when the sides met last season, which more than likely played a part in Vern Cotter's selection.
The best example from the 2014 game would be this second half scrum, where Grant gets in low and straight, catching Ross off guard. With the ball fed, watch the excellent body position of Grant below, who is perfectly square and straight to Ross opposite him.
Watch the difference in the pair's height. Grant is considerably lower, while Ross has arched his back, and loses all his power.
It's worth noting that while the Scottish scrum had real difficulty in the second half against England, they looked strong throughout on the loose-head side, with Dickinson handling the powerful Dan Cole excellently.
On the opening scrum of the day, Dickinson showed terrific technique to keep the scrum stable and upright, despite Cole's attempts to pull him to the ground.
In the picture below, we can see how Cole is bound on Dickinson's arm, and dragging him downwards, but the loose-head keeps his body shape perfect, while at the same time giving up very little ground.
As we can see below, Cole binds directly onto the arm of Dickinson, with the X marking where a safe and legal bind should be.
We can see that he opts to wheel, popping out his hips and driving inwards. It's an illegal move, which he was penalised for, but he could certainly argue the first infringement was from Cole.
It was an easy spot for the Frenchman, with Marler making absolutely no attempt to drive square and straight. In the aerial shot below, just look at the difference in angles between Marler and Murray (top), and Cole and Dickinson (bottom).
This aerial shot a couple of seconds later shows just how far it moves to the side, and how little it moves forward. The lines of the pitch are a great aid to judge off.
It's often argued that all loose-heads will naturally drive across the scrum, but that theory is complete rubbish. Often times there will be a slight angle, which is acceptable, but in each of these examples, Scotland's Alasdair Dickinson shows that it is possible for a loose-head to scrummage effectively without the need to bore across.
Poite had cottoned on to Marler's angles, and another penalty for a crooked drive followed. However, this was just what Marler needed, and when he corrected his angles in the second half, he exposed a real weakness in Murray's game.
Putting Murray under pressure, Scotland were incredibly lucky not to be penalised after Rob Harley bound to his prop and drove in on Marler.
In this shot just as the ball is about to be fed, note two things. Firstly, keep watch how Marler is now lined up straight against Murray, and watch how Harley, circled, is bound correctly to the second row of the scrum.
But once Marler begins to get a nudge on Murray, it prompts Harley to remove his bind from the second row, and drive in on Marler, essentially acting as a fourth prop. We've seen this move several times so far in the Championship, and it's something that is highly illegal and dangerous. Watch below how he shifts his bind from its original spot, the X, up onto his prop, circled.
For reference, we'll show a shot of how the scrum lined up as they engaged. Note the line running through its centre.
Murray got his body position all wrong, sitting back onto his heels as Marler came forward straight on.
While Marler struggled initially against Murray, it was largely down to his own technique. Once he corrected his angles, the English scrum went forward at will, and it's an area that Cian Healy can target this Saturday.
Equally though, Ryan Grant held things together on his side when he was introduced last weekend, and troubled Mike Ross last year, while Alasdair Dickinson coped relatively well against Dan Cole.
The individual battles between Ross and Grant, and Healy and Murray will dictate the scrum this weekend. Chances are, it'll come down to which loose-head dominates more.
Our money is on Healy.