At some stage in the Six Nations the Millennium Stadium roof was going to have an airing. Or not, since Scotland want the sliding shield against the rain kept in its bays for as long as possible before they face Wales.
Warren Gatland, the coach of the home team that would prefer a dry surface, has put aside his pre-match diplomacy of the build-up to the England game and had a swipe at Scotland. I trust it is feigned irritation, because there is no logic on earth to explain why Andy Robinson, coach of the weather-washed Scots, should even begin to accommodate his opponents' wishes for a firm, dry surface.
On the day itself, should rain fall, the roof will be closed, but Robinson wants Gareth Williams's first throw into the lineout to be as difficult as possible. And the sooner Scotland can make the ball greasy for the hooker the better.
A lot of individual and collective Welsh confidence will hinge on the flight path of that first throw, as Williams tries to find one of his jumpers, presumably a long way away, towards the tail of the set piece. Jonathan Thomas is an athletic stretcher, as is Alun Wyn Jones, both more conditioned to the middle or back of the lineout than perhaps the flatter, bumpier jump at the front.
There is a gamble to the Welsh selection, stacking the options at the back – all three of the back row serve as jumpers, including Martyn Williams – in order to try to provide ball off the top, to feed Jamie Roberts. Wales are devoted to hitting the gain-line in about three seconds.
It remains a frustration that the centre can shine for the Lions and the Barbarians, but find himself shackled in his own land. Once, he was stopped by Joe Worsley. Last week against England he was starved of lineout possession.
The danger for Wales is that if they have to settle for more laboured possession from the front of the lineout it may mean putting Andy Powell or Ryan Jones down there, which limits the options of what to do with already compromised ball. For a side committed to a high tempo, Wales may have to start with their feet in mud, and not just because Scotland have insisted on letting mother nature in.
Scotland had problems of their own in the opening round, with their scrum taken apart by the French. Euan Murray returns to offer reassurance in that department, and with him on the Scottish tighthead and Adam Jones on the Welsh, it would appear that nothing is going to shift either one way or the other quite as alarmingly as Scotland buckled on their own put-in in round one. The first scrum feed, though, will be as intriguing as the first Welsh lineout.
Even if Scotland secure solid possession can they score enough points? Chris Paterson on the day he earns his 100th cap is going to be as accurate as ever, but will even seven penalties be enough? Wales are going to score lots of points, with AW Jones offering a man-of-the-match performance by way of penance for his Twickenham trip, and James Hook developing from solo performer to leader of a quartet, with Roberts, Lee Byrne and Shane Williams joining in. Wales 36 Scotland 21.
This is an excerpt from The Breakdown, guardian.co.uk's twice-weekly free email on the Six Nations. Sign up now!