It happened for the first time in the 17th over of Sri Lanka's innings. Mohammed Shami, landing the ball in the fourth-stump channel and, as he almost always does, hitting the seam, squared up Angelo Mathews and found his outside edge. The ball flew into the gap between second slip and gully.
The ball bisected those two fielders once again in the 21st over, and then, when Shami returned for another spell after tea, in the 36th over. If there was some doubt over whether the first two edges would have carried to a hypothetical third slip, there was none with the third: it went at chest height.
It was that kind of day for Shami. It was that kind of day for India.
For most of India's innings, Sri Lanka's quicks had bowled to a field that included at least three, and often four, slips, and sometimes up to two gullies. India, however, couldn't always respond in kind.
Sri Lanka's fields had a lot to do with India losing half their side by the time they had put 50 on the board. There were no top-order partnerships to force Sri Lanka even marginally onto the defensive. They also had something to do with the conditions on days one and two: a green, damp pitch, and an uninterrupted expanse of grey cloud overhead. The ball swung and seamed all the time.
It was different now. The sun had broken through some ten minutes into the third morning, bathing Eden Gardens in an unearthly glow and causing spectators to shield their eyes from the dazzle of the players' whites. While the ball continued to seam around, it did not swing as much without the cloud cover.
India, moreover, were protecting a total of 172, and Sri Lanka had got off to a quick start, thanks to Sadeera Samarawickrama's aggression and marginal errors in line and length from a pace attack that strove perhaps a touch too hard for early wickets. When Mathews edged between second slip and gully for the first time, Sri Lanka were 65 for 2 and going at nearly four an over.
India had to control the scoring as well as push for wickets, and that meant one fielder in the covers and usually one at square leg or midwicket. The presence of an extra leg-side fielder may have even helped India bowl closer to off stump than Sri Lanka did. They certainly made the batsmen play time after time.
On this day, they kept playing and missing, and Wriddhiman Saha kept making shoulder-high collections behind the wicket. At some points, particularly when Mathews and Lahiru Thirimanne were putting on a battling and not-always-convincing 99 for the third wicket, it felt as if Shami, Umesh Yadav and Bhuvneshwar Kumar could have bowled slightly fuller to try and convert some of those plays-and-misses into edges, but there wasn't a whole lot wrong with their lengths in the first place. It was simply a day of fine margins.
When the ball did kiss the edge, it proceeded to sneak into gaps. Once, when Thirimanne was batting on 27, he nicked Umesh to first slip, where Shikhar Dhawan shelled a straightforward chance.
It was that kind of day for India.
Finally, in the 37th over, their pent-up frustrations found a moment of release, when Virat Kohli dived low to his left from second slip to send back Thirimanne for 51. He held on to the catch, got up on his feet, and speared the ball into the turf next to him, very nearly endangering Saha's toes.
The crowd at Eden Gardens, which had grown from modest beginnings to around 10,000 by the start of this final session, roared. They would not let up until bad light brought an early end to the day's play. By then, the clouds had returned, and Shami, in particular, looked like taking a wicket every ball, seldom wavering from that boa-constrictor fourth-stump line and zipping past both edges of the bat.
It was Umesh, however, who dismissed Thirimanne and then Mathews, who, failing to get to the pitch of a drivable ball, scooped a catch to cover.
It was that kind of day for Shami.
It ended prematurely, five balls into his 14th over, when he trudged slowly off the field, clutching his thigh. He had struggled with the humidity of his home ground even during his first spell with the new ball, and it seemed like cramp rather than anything more serious.
The team's media manager confirmed this after the day's play, and said Shami was expected to be back on the field on Sunday.
India will definitely need him. Their lead is now down to seven runs, and they still have six wickets left to take to try and minimise Sri Lanka's lead. For this they will need all their bowlers fit and firing on what could be a pivotal fourth day.