"Hopefully he's not born while I'm over there. I'm pretty nervous but it's exciting at the same time," Coles said as he prepares to play Argentina in Napier on Saturday.
"From a personal sense, it was an easy decision to make [to miss Springboks test], but when I look at the rugby side of things, it's a tough one to swallow, I suppose. But I've got no regrets about it, my decision has been made."
Coles has started every test this year for the All Blacks, quickly consigning Keven Mealamu to a back-up role. But while he is now clearly the best hooker in the country, the lack of real depth in the position remains a slight concern.
Steve Hansen has put his faith in 22-year-old Harris as the next best, and Coles said the Chiefs player was progressing nicely.
"He's come a long way. He's been good in the environment. Looking back, I can see a bit of me in the guy... I'm not saying I'm old or anything... but he shows a lot of promise and I suppose the best way to go about it is just get out there."
It's a path that Coles has trod. A specialist ball runner, some added weight and upper body strength has give him extra confidence and effectiveness in the tight. Noticeable in the big win over Australia at Eden Park was his work in the dark places as well as the open.
"All last year I don't think I was big enough to dominate," he said. "Adding that extra bit of weight and physicality really does help. It does wonders for your game and it gives you confidence as well that you can really match it with the big boys as well, that you can test yourself against the best teams in the world.
"It's about working hard and making sure you can carry that weight but being dynamic at the same time."
