Tom Curran says he is a "work in progress" as he bids to perfect the art of death bowling and secure himself a place in England's squad for their home World Cup in 2019.
The 22-year-old is part of the squad playing in New Zealand, and helped them secure a nail-biting, four-run victory on Saturday to go 2-1 up in the five-match ODI series.
England could secure an unassailable 3-1 lead in the series when they face the Kiwis in Dunedin on Tuesday, live on Sky Sports Cricket from 9.30pm, and Curran will once again be looking to help his country to victory with his bowling late in the innings.
He said: "You have time in training to get a feel for all these different slower balls - and if you don't try them, you're not going to learn. It's a gut instinct, and out there I make a decision and commit to it.
"I'm practising all the time, trying these new ones. There's obviously the knuckleball, and there are other slower balls that are coming out.
"In games at the moment, I'm just using the two. But there'll be a couple more interesting ones coming out for the season - a work in progress.
"I think you've just got to try things.
"A couple of years ago I just started practising different types of slower balls from the back of the hand, and they seemed to work. A combination of that and the off-cutter seems to be coming off."
England are ranked third in the ICC's ODI rankings, but will go into the World Cup on home soil next year as one of the favourites.
Curran is hoping to be part of the squad, and said: "That's exciting - it's a great place to be in. It's about me putting my hand up and performing when I do get given a chance.
"It's 15 months away, so I'll finish this tour, go back, do my thing for Surrey and hope to give Morgs a tough selection problem."
Hear more from Curran in the video at the top of the screen as he talks to Sky Sports' Ian Ward ahead of the fourth ODI.