If England go on to win 19 in a row, the challenge for the All Blacks becomes to win 20. England, obviously, are a threat to the All Blacks' number one standing, but that, in a curious way, also make them an opportunity, too.
An opportunity for the All Blacks to ask themselves how hard they are willing to work? Can the All Blacks match England for sheer will power, because it was commitment and belief that enabled the latter to squeeze past France and Wales in recent weeks?
Can the All Blacks match England's physicality? Can they keep finding ways to sharpen their attack? These are questions the All Blacks ask all the time, but with another team breathing down their neck, delivering definitive answers on the field - well it sharpens everyone's desire and focus.
There are other good reasons why England are worth cheering on. They are filling the hole left by South Africa and to a lesser extent Australia. The former were a travesty last year and having decided to continue with coach Allister Coetzee, it is hard to see them being much better this year.
The Wallabies still don't have the ability to consistently perform and it felt like the All Blacks weren't really pushed throughout the Rugby Championship last year. It was all too easy and life only got really tough for the All Blacks when they played Ireland and France.
England look to be up another level again and who doesn't want to see the All Blacks taken to their limits or even beyond trying to find a way to beat a team that is their equal?