There's a lot more to it, of course, but at its deadliest, Tim Southee's method is all about that old three-card trick: outswing, outswing, and the one that goes the other way.

Except it isn't just the "one" that goes the other way, but three different ways of delivering a ball that moves into the right-hander.

Take the second-innings wickets of India's openers in the World Test Championship final in Southampton. Both were lbw, playing for non-existent outswing, but the balls that dismissed them were entirely different.

Shubman Gill, first to go, was out to Southee's well-known three-quarter-seam ball, which is delivered with the seam scrambled, and moves into the right-hander off the pitch. Rohit Sharma, however, was bamboozled by something that hasn't been seen all too often.

Every now and again on this tour of England, Southee had delivered the traditional inswinger, with the seam canted towards fine leg, but most had come out of the hand noticeably slower than Southee's stock ball. The ball to Rohit wasn't the traditional inswinger; the seam was canted towards slip, like it is for an outswinger, but the ball was flipped around so its rough side - this was the 27th over of India's innings - was facing the leg side. And unlike Southee's attempts at bowling the genuine inswinger, this one came out at normal speed.

It's entirely possible that Rohit saw the seam position, judged the ball to be leaving him, and decided to shoulder arms. Instead, it veered in towards the stumps and struck Rohit's front pad.

The Dukes ball that is used in England moves significantly more - in the air and off the pitch - than the Kookaburra that's used in New Zealand, and this allowed Southee to try and develop the inswinger on this tour.

"I think all players in any sport are always looking to try and get better and looking at ways you can improve your game," Southee said in a media interaction on Monday. "I obviously don't have express pace, so you're looking to skin the cat differently, and that's using subtle variations and I obviously rely heavily on my outswing, but with the Dukes ball and the ability to move the Dukes ball a little bit more than what you can with the Kookaburra, a lot of work went in, leading into that series, about just trying to get the ball to move both ways."

Shane Jurgensen, New Zealand's bowling coach, said Southee came up with the new variation during the camp New Zealand held in Lincoln before they left for England.

"I actually think that wicket of getting Rohit out was a long time of Tim trying a few things and always trying to improve," Jurgensen said. "I think that goes for every bowler in our group and I think that's really stood out more in the last two years. It has always happened, but I really think it really started in our camps in May at Lincoln, when he was playing around with bit of an inswinger and it was good.

"It took him a while to sort of get it and all of a sudden he learnt of possibly turning the ball around the other way and bowling it the exactly same way. [It] probably has a little more pace on it compared to the [traditional] inswinger and I think that's been a credit to Tim.

"He's always looking to improve and he's been such an outstanding performer for New Zealand for such a long time; 600-plus wickets for New Zealand now and that breakthrough of Sharma was at a really crucial time. In fact both of those wickets were, to give us a chance to get Virat Kohli in early."

Karthik Krishnaswamy is a senior sub-editor at ESPNcricinfo