Vunipola’s three-match ban was reduced to two matches after the succesful completion of World Rugby’s coaching intervention programme.
The programme, known informally as “tackle school”, can only be completed once in a player’s career to earn a week off a levied sanction, and is performed alongside a coach.
England defence coach Kevin Sinfield, who has also taken Owen Farrell and Tom Curry through the programme this year, was alongside Vunipola as the number eight went through the programme.
And though suggesting it was like “sucking eggs” at times, Vunipola believes he has come out with a better understanding of how best to tackle.
“Kev is very well rehearsed in running those tackle schools, which is probably not a good thing for me to say,” Vunipola, who returns to the England starting side against Chile, joked. “For me it did feel a bit like sucking eggs but it taught me a lot in terms of my technique.
“[Sinfield] is very good at his job so it only took us one time to do because when you do it you have to film it. I learned a lot about using my arms, and the biggest thing was lowering my height.
“I am such a big guy, [so] I am so used to using my body as a mechanism to stop someone rather than technically getting in the right position. It was good for me so hopefully you won’t be seeing any of that any more.”
With Owen Farrell also dismissed during the warm-up fixtures, and Tom Curry sent off in their opener against Argentina, England’s tackle technique has been under scrutiny.
Sinfield insists England are continuing to work hard in that regard, though admits that sometimes “people get it wrong”.
“We practice tackle skills most days, in short blocks, and we are very smart in the risk and safety and how we employ it,” Sinfield outlined.
“The tackle school has a most specific nature to it. Billy was outstanding in the work he has done, we have just completed Tom Curry’s as well.
“I have done a number of them now but these guys are humans and when they are in a competition like this and intense as this, unfortunately players are going to make mistakes. We try and help them and keep working with them.
“We are seeing this at elite level but it is grass roots where we have got to be helping people and keep pushing tackling, and also understand that sometimes people get it wrong.”