Teams that will contest the Rugby World Cup semifinals this weekend keep few secrets from each other.

England and New Zealand, Wales and South Africa have played each other often enough, have studied each rival's form so thoroughly, have subjected their opponents to such microscopic analysis that little guesswork remains.

The semifinalists have reached this point through steady improvement and the overwhelming aim of every team will be to do even better in the semifinals the things they do best most of the time.

But that doesn't rule out the possibility there will be some surprises when England plays New Zealand on Saturday, when Wales plays the Springboks on Sunday. Each team is likely to have worked on small aspects of their play that might take the analysts by surprise and catch their opponents off-guard.

Both semifinals will be tight, and a moment of innovation could succeed in circumventing an opponent's careful preparation, for instance in the match between Wales and South Africa.

Wales has won its last four matches against South Africa but hasn't recently played a Springboks team of the caliber of the current side. The match appears to be a contest between a team that doesn't score many tries and one that doesn't concede many.

Wales scored only 10 tries in winning the Six Nations title this season, equaling the lowest tally in history by a Grand Slam winner. It ranked last in the tournament for line breaks, broken tackles and meters run.

South Africa has conceded only one try in its last four matches and hasn't conceded more than two in any test this year. It has given up only 11 points per game in 2019, it's lowest average in almost 50 years.

Wales relies more on kicking goals than scoring tries, landing a record 16 penalties during the Six Nations. Goalkickers Dan Biggar, Rhys Patchell and Leigh Halfpenny all have success rates in excess of 80% at this World Cup.

That helps Wales do what it does best, get in front and stay in front by holding onto the ball. Wales has conceded fewer turnovers than any other team in the semifinals. Its Achilles heal may be that while it consistently wins when it scores first, it wins around 40 percent of the time when it doesn't.

That challenges South Africa to get on the board first; significantly it failed to score a try in its first pool match against New Zealand when it dominated possession for most of the first quarter.

South Africa's problem is that it turns over possession more often than any of the other semifinalists and its goalkicking success rate is the lowest of the remaining teams.

Its strengths are its set piece, its kicking game and its ability to leverage those qualities. Forwards coach Matt Proudfoot said South Africa plays "in a specific way and the players have confidence in that, knowing their roles and what is required of them. They thrive in executing it."

That seems to reject innovation and while South Africa will likely keep up its aerial barrage, Wales may see Boks flyhalf Handre Pollard step out of the pocket and move the ball by hand more often.

England coach Eddie Jones also appears to have rejected the idea of his team introducing anything new in the semifinals.

"For 2½ years we have been building up a game to play New Zealand, so we don't have to bring a lot of new stuff into our game this week," he said. "There's a certain sort of game you have to have to play against New Zealand, and certainly we have tried to incorporate that into our tactical armory."

Some aspects of England's game are set in stone; it has kicked more and gained more kick meters than any other team in the World Cup and a majority of those are into open space.

But the selection of George Ford at flyhalf suggests England realizes it may have to do more against an All Blacks team which has averaged more than 43 points per game in 2019 and leads the World Cup in points scored, tries, line breaks, broken tackles and offloads.

New Zealand signaled a slight tactical change by selecting Scott Barrett, usually a lock, at blindside flanker to give it a taller lineout and bulkier back row. That adapts it more to England's style.

That acknowledges it may have to tough it out on Saturday and earn the right to use its backline. The ball may be longer on the ground than it was in New Zealand's quarterfinal win over Ireland, and the All Blacks have adapted to that challenge.

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