If Nuwan Pradeep has ever had a word with a batsman, it is possible his voice did not carry to the other end of the pitch. Chances are, it has never happened anyway. Not only is Pradeep perhaps the most withdrawn man in international cricket (he has played 23 Tests, but how many times have you heard him speak?), he is also a sporadic presence in this XI, and so, rarely capable of building himself up to some professional confidence.

That he's injury prone is not even slightly his fault. Pradeep comes from difficult circumstances, and coaches have suggested there was a lack of protein in his diet during adolescence.

But however the problems have come about, Pradeep's hamstrings now almost audibly twang with each bouncing step towards the bowling crease, so perpetually close are they to snapping. Such are the travails of Pradeep's life. Even when he is fit, he sometimes does not make the XI, especially at home, where Sri Lanka sometimes only deploy seam bowlers in order to protect themselves from nastier questions about the state of the pitch. Pradeep comes to us intermittently, and sometimes unexpectedly, like a substitute teacher in high school - never really sure about his position, but grateful for the chance to be there.

Sometimes he is so mild mannered, by the end of the period kids are hanging off the ceiling by their underpants, and have tattooed rude pictures on each other.

But on other days, such as this one, Pradeep picks up the pointer, slams it on the desk and makes the world take notice. The Sri Lanka staff room remains an unhappy place, as it has been throughout the series, but thanks to the bowlers - Pradeep and Lahiru Kumara in this innings - they will avoid being sacked en masse when they face the higher ups.

He had begun on day two as meek as ever - short and wide to Faf du Plessis, and duly thunked to the square fence. He'd concede another four that over, but upon his return to the bowling crease, Pradeep was strikingly changed. The first ball of his second over pitched on off and veered sneeringly away from du Plessis' bat. The next one was almost as good. The third delivery squared him up to take his edge, and suddenly, while Pradeep's larynx remained as still as ever, but man, had his bowling had found its voice.

In an 18-ball burst beginning with that du Plessis wicket, Pradeep was transformed from subdued substitute to the kind of headmaster that has a nose which smells contraband chewing gum from miles away, and a stare that makes students wet themselves. There were cynical, threatening, whispers from the ball, as it beat edge after edge; his co-faculty members in the slips howling their appreciation of the dressing down this unruly South Africa batting order were receiving. These batsmen had run amok this series. Pradeep took four wickets for one run, bowled a brute that pounced off a length at Vernon Philander, and gave Sri Lanka some satisfaction, short-lived though it turned out to be.

But as it so often happens in the teaching world, after lunch Angelo Mathews came in like a school director attempting to piggyback off Pradeep's excellent work, opening the bowling from Pradeep's end. When Pradeep finally got the ball in hand and tail-end batsmen to bowl at, he found himself completely under-resourced - he squared Wayne Parnell up and took his edge, but only one slip was in place to a bowler in sublime rhythm. The diving man at first slip couldn't hold the chance.

"I was hoping Pradeep will take five wickets in an innings, because he hasn't done that before in Test cricket," bowling coach Champaka Ramanayake said. "He bowled pretty well in the last game also, though he didn't pick up any wickets. Today morning he hit the right length consistently. Hopefully he will get more wickets in the second innings."

There may not be much of a second innings, of course, with Sri Lanka 80 for 4 already, and South Africa's quicks smelling blood on a pitch that is still very quick. But at least before the mandatory collapse set in, Pradeep's 18 balls provided a sliver of Sri Lanka dominance. It was probably their best patch of play in the series, and all the sweeter for having come from the mellowest man on the staff.