It usually happened when West Indies' fast bowlers hit the short-of-good-length area in the corridor outside off stump. Rahul would push his bat at the ball, and then, having made contact, withdraw it hastily, as if he'd just touched a blazing skillet.
He'd been out playing the same sort of half-shot in the first innings, getting squared up by a ball from Jason Holder, nicking to first slip, and then pulling his bat away futilely with an elaborate flourish.
Batsmen often shadow-practise the shot they should have played after they are beaten or dismissed; with Rahul, the shadow-practice seems to begin as soon as he's made his mistake, as if to say, "wait, I've taken that shot back!"
His dismissal on Sunday was a little different, off a front-foot defensive shot to a delivery from Kemar Roach that left him late in the corridor. But again, his bat, having felt for the ball, shrunk back guiltily after edging it.
Rahul didn't look like he was simply watching the ball and reacting to it. He seemed preoccupied with thoughts of where his feet were, where his head was, and how his bat was coming down.
The uncertainty was understandable. Since the start of 2018, Rahul has averaged 22.23 across 15 Test matches, scoring one hundred, against England at The Oval, and one fifty, against Afghanistan in Bengaluru. His career average, which stood at 44.62 before this lean run, has now slumped to 34.58.
In that time, he's made a few technical adjustments, possibly prompted by a run of nine straight innings - in England, and against West Indies at home - in which he was either bowled or lbw.
The most visible change is in the pick-up of his bat. In 2017, and through most of 2018, Rahul's bat used to point to first slip at the point when the bowler let fly. During the Australia tour at the turn of the year, his pick-up became a little straighter, with his bat pointing over the top of off stump, perhaps to ensure that he didn't leave too big a gap between bat and pad. The change didn't bring him any immediate reward - he only managed one double-digit score in five innings.
KL Rahul has changed the way he picks up his bat, and the extent of his trigger movement. It hasn't changed his Test-match fortunes, just yet. pic.twitter.com/49CMISIIKS— Karthik Krishnaswamy (@the_kk) September 1, 2019
On the West Indies tour, he's been holding his bat up even straighter, over the top of middle and leg stumps, and his back-foot trigger movement isn't taking him as far across his stumps as it used to.
His indecision in the middle suggests that he's still getting used to his new technique. It can't be easy to be playing international cricket with a set-up you aren't fully comfortable with, but that's the way of the modern game - particularly if you're an India player - with no off-season and hardly any gaps between series to fine-tune your game.
India might have given him a break here if their other first-choice opener had been available, but Prithvi Shaw's suspension has almost forced them to pick Rahul. And with the ability he has, he isn't an easy batsman to leave out in the first place.
Rahul's struggle is hard to watch, and it must be even harder to experience. But hidden somewhere amid all the indecision is a top-class batsman who not too long ago made ten 50-plus scores in the span of 14 Test innings. India will hope Rahul can rediscover that batsman sooner rather than later.