Finance Minister Michael Cullen was on his feet and in the middle of answering question three during question time on Tuesday when he saw National leader John Key across the chamber nodding his head, and noted it.
"Last year I was attacked almost daily by the members opposite - Mr Key nods his head in agreement - for doing precisely that," Dr Cullen said.
In fact, Mr Key was nodding at Prime Minister Helen Clark in response to a note from her that a messenger had just delivered asking to meet him out the back of the House when the question was over.
Five minutes later it was, and the two leaders ducked out.
Helen Clark handed Mr Key a copy of the amendment to the anti-smacking bill that was revealed yesterday in an unprecedented joint press conference between the leaders.
They agreed that Mr Key would get back to her later on Tuesday night.
Helen Clark headed back to her office on the ninth floor of the Beehive.
Mr Key went back into the chamber and immediately pulled out deputy leader Bill English and strategist Murray McCully to discuss it in the back room.
The compromise explicitly tells the police not to prosecute inconsequential "offences", as opposed to just hoping they would not after the bill is passed.
The early thoughts of the MPs in the back room were that while it was not perfect, it was close to what Mr Key himself had put to the mover of the bill, Sue Bradford, last week. Mr Key consulted his head researcher, Phil de Joux, and his chief of staff, Wayne Eagelson.
At 8.30 that night, Mr Key and Mr English paid a private visit to Helen Clark's ninth-floor offices. The PM was busy with a team of officials in her ordinary meeting room so they were taken to a smaller meeting room with the woman they sometimes call "H2," Heather Simpson, Helen Clark's chief of staff.
H2 made them coffee and Helen Clark left officials to join them and listen to their agreeable response. They then discussed how to present it, canvassing the idea of Helen Clark and John Key jointly moving the amendment.
Dr Cullen, as Deputy Prime Minister and Leader of the House, was called up to see if that was possible, but it wasn't. So United Future leader Peter Dunne was telephoned by Helen Clark and was made an offer he couldn't refuse - to move the cross-party amendment.
It wasn't Dr Cullen's first involvement in the compromise. On Monday of last week, he found himself unexpectedly dining with Mr Key.
The pair were in Sydney for the Australia New Zealand Leadership Forum. Someone had the novel idea of seating the two arch-rivals together at dinner at the Intercontinental.
The week before, Mr Key had raised in a speech to the Salvation Army the prospect of cross-party discussion to find a way to act on what he saw as a common view, that there should be no prosecution of light smacks.
He was planning to meet Sue Bradford 36 hours later to take to her a new compromise.
Mr Key and Dr Cullen chewed it over at the dinner.
Labour, which has been suffering badly in the polls lately, took a lot of interest at the outcome of the Anzac Day Key-Bradford talk.
Ms Bradford rejected Mr Key's proposal, an amendment that would allow "minor and consequential" smacking of children, because she could not countenance a description of the level of violence against children that was acceptable.
But it was clear Mr Key had moved notably in that he did not oppose the bill's intention to outlaw force for the purpose of correction.
The next day Helen Clark was picked up from home about 6.30am. On her way to the airport for a flight to Timaru she called her old friend and former Prime Minister Sir Geoffrey Palmer, now president of the Law Commission, from the back of the Crown car.
He had personally advised the select committee and had drafted both the wording adopted by the committee and version promoted by National MP Chester Borrows.
She asked him to try again, given that she, Mr Key and Ms Bradford all agreed that parents should not be prosecuted for trifling smacks.
The law drafters in the Parliamentary Counsel Office were put at his disposal.
Sir Geoffrey rang her back Friday night with a suggestion that would encompass Mr Key's word "inconsequential." It effectively said police need not prosecute any offence considered to be so inconsequential there was no public interest in doing so.
Helen Clark rang Dr Cullen on Saturday morning. On Sunday she talked to Mr Dunne about it and more importantly, Ms Bradford, who was amenable to it.
When Helen Clark's Cabinet traipsed into her office at 10.30 on Monday morning for their usual pre-Cabinet discussion, she told them a compromise was being worked on.
All others that supported the Bradford bill were then contacted. Bradford liaised with the Maori Party and found accord. Likewise Social Development Minister David Benson-Pope contacted Brian Donnelly and Doug Woolerton from New Zealand First.
Helen Clark had everyone lined up. Then she scribbled her note to Mr Key from her desk in Parliament on Tuesday afternoon.