On the third morning of the Indore Test, Ishant Sharma snuck through Shadman Islam's defence and hit the top of the middle and leg stumps. It was another testament to the levels at which India's fast bowlers are operating at right now because, it turned out, Ishant had successfully trialled a new variation in the middle of a Test match when he did that.

Ishant constantly tested Bangladesh's left-handers in the corridor from around the wicket in the first innings, swinging the ball away from them and regularly past the edge on a green, bouncy first-day pitch. Over the last year or so, he has become known for his effectiveness with this mode of attack. He removed the left-handed Shadman with a full, away-going ball eventually, getting him to drive and edge behind.

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In the second innings, he set Shadman up in the same way, angling the ball into him and curving it away, before getting one to nip in off the pitch, beat his inside edge, and hit the stumps. He had only thought of bowling that ball - which doesn't come naturally to him - on the previous day.

"Actually, he started working on that variation from yesterday," India's bowling coach Bharat Arun said after India had won by an innings.

Ishant had been spotted bowling alongside Kuldeep Yadav and R Ashwin during the tea break on day two. "If you look at the way he signalled after he got the wicket, he was very happy that he could do that," Arun said. "Each time you try to explore new avenues in your bowling, you constantly look to improve. And this would give him the much needed fillip to experiment more and try out."

A majority of Ishant's bowling to left-handers took place during his first spell, and it helped that he had 20 balls at Shadman in his first four overs. All of them were delivered from around the wicket.

One of the reasons Shadman was picked in this Bangladesh squad was for his ability to leave well outside off stump. This was in evidence in the first innings before he was lulled into poking away from the body. On the third day, he looked determined to lean on that strength. And, having seen Ishant's usual movement away and the good bounce the pitch still offered, he looked fairly confident while leaving deliveries that were straightening from close to an off-stump line.

Ishant celebrates the wicket of Shadman Islam BCCI

Ishant's first few attempts at landing his new variation were hit-and-miss. One to Imrul Kayes went down the leg side, and the next one was tickled easily to fine leg. Then, in his fourth over, he had a proper go at it. The first ball left Shadman and was left alone. The next four came in - two were overpitched and worked into the leg side. Between those deliveries, there were two that rose up and hurried Shadman. They were acknowledged by his captain Virat Kohli, with a thumbs-up and a nod as if to say, "that's where you need to be".

The signals all make sense now. When Ishant burst through Shadman's defences off the last ball, the batsman was defending for a corridor line and lost his leg stump. Ishant was wider on the crease, but it looked like most of the action happened with his wrist. Ishant's release is generally upright, and his fingers come down hard on the inside half so that the ball can move away from the left-hand batsman. On this occasion, it looked like the fingers merely grazed the inside half, but with the wrist still as upright as ever. In essence, it was a subtle legcutter. A scrambled seam wouldn't have helped things for Shadman either.

It was another big stride for a bowler who has had something of a delayed, yet accelerated, growth over the last few years. Ishant has become stronger, made batsmen play more often, swung the ball a lot more through a subtle change in his delivery position at the crease, and even developed a knuckleball earlier this year, between the Australian tour and the IPL.

In an interview with The Cricket Monthly last month, Ishant was asked if he didn't think his new approach to left-handers - angling in and swinging away - was a touch predictable.

"With that angle it is very difficult for the batsman to leave the ball," he had explained. "The batsman thinks that the ball is coming close to him, but with my action the ball is moving away. He has that fear [at the back of his mind] that if the ball goes straight, it can hit the stumps. To make sure that he does not let happen or get lbw, he feels he has to play that ball. That is why that angle is dangerous."

It seems now that, in the space of a day, he has at least hinted at adding a new dimension to that danger.