Expect even more relentless repetition of upbeat language than usual from Prime Minister John Key and Labour leader Phil Goff as the worm returns for tonight's leaders' debate on TV3.
The debate will use the Roy Morgan Reactor, more commonly known as "the worm", to measure the response of a studio audience of undecided voters selected for a balance of gender and age.
They are given a hand-held dial about the size of a computer mouse which they rotate to the right if they like what they're hearing and seeing from whichever leader is speaking - or to the left if they don't. Responses are compiled and rendered as a line or graph on the screen.
"They react quite emotionally. They're not thinking rationally," says Roy Morgan Australia chief executive Michele Levine.
She says success in charming the worm is a good sign of how the leaders are connecting with voters but it's by no means a definitive guide as to whether they are influencing voting decisions.
Nevertheless, United Future leader Peter Dunne's success in moving the worm upward by repeating the words "common sense" and "family" during a 2002 debate was considered a factor in his party winning eight seats in Parliament, its best ever showing.
Ms Levine expects New Zealand voters will react the same as those in Australia and the US by rewarding positive messages and behaviour rather than attacking tactics.
This year, viewers will be able to go online about an hour after the debate and replay it with the worm selected to reflect the response of particular groups within the audience, for example just women or just those who have previously voted National.
TV3 and Roy Morgan invite viewers who have an iPhone, Android mobile, iPad or tablet device to participate.