They pray for cloudy weather, they suck boiled sweets and they shine one side of the ball as though their lives depend upon it.
Cricketers will do just about anything – within the laws, naturally – if they believe it will cause those five-and-a-half ounces of red leather to deviate while moving through the air. Even a Nasa scientist, Rabindra Mehta, has devoted more than 25 years of study to the subject.
The debate will continue, but we can all agree that there are few more enjoyable sights in cricket than watching an expert swing bowler practise his art under skies of 50 shades of grey and with the temperature not quite high enough to justify removing your coat.
Jimmy Anderson is perhaps its best exponent, and this match has been a celebration of his skill. On Friday he became only the fourth English bowler to claim 300 Test wickets, and yesterday was another triumph. Three more gave the Lancastrian his 13th five-wicket haul in the long form of the game, and gave England the lead, which they could hardly have hoped for after their sleepy first innings.
Yet Anderson is not the sole master of swing in this game. Trent Boult, New Zealand's highly impressive left-arm seamer, has removed Alastair Cook twice in this match, and four times in as many Tests. Boult won the mental battle yesterday, tempting Cook to drive at a ball that was moving away from him. Dean Brownlie clutched the ball at third slip; Cook swished his bat in anger.
The reaction was telling. Cook prides himself on his ability to break a bowler's spirit through patience and self-restraint. Against clever swing bowlers who possess the same virtues, these battles will sometimes be lost.
For a batsman, the anticipation of swing can become as damaging as the reality. Uncertainty had flowered in the mind of Nick Compton to such a degree that when Neil Wagner brought one back down the slope the opener was hesitant, allowing the ball to sneak between bat and pad and remove the off stump.
But if a batsman can find a way through those spells when bowler and ball beguile them, the rewards are clear. Jonathan Trott and Joe Root did so and built a century partnership, the first of the match and an alliance that could prove decisive.
That's the thing with swing: now you see it, now you don't. Here, you sense, might lie the limitations of this New Zealand attack. Boult, Wagner and Tim Southee, who returned with three wickets late in the day, are skilful bowlers; when conditions desert them, so their weapons are blunted a little.
When the ball isn't swinging a bowling attack can appear predictable, which England cannot be accused of being in this match. With Stuart Broad and Steve Finn, you never quite know what you will see.
Finn is learning but more consistency is expected of Broad, a Test regular for five years. He was as purposeful and accurate yesterday as he was distracted and wayward on Friday, when he bowled too short and was treated without mercy by Ross Taylor.
On the third morning, Broad had practised finding a full length before play and set the pattern for the day by producing a wicket maiden in his first over. The victim was Brendon McCullum, the tourists' captain and probably their most dangerous batsman.
It was the gateway to England's best day of the Test, at least until they lost four wickets for 12 runs in the last hour. When both teams have men who know how to move the ball, it remains very difficult to predict which way the match and the series will swing.