In my varied matrimonial life, there was one pair of in-laws I had who for years conducted a sophisticated psychological war against each other. The game was for each to get the other to lose their temper while appearing themselves to be sweet reason. The quiet, intelligent voice was a particular weapon – it could start a fist fight over a christening font.
Ed Miliband is using that voice and it works very well. It is annoying without being an obvious attempt to annoy. And Cameron, surprisingly for one so practised in the arts of common-room taunting, is falling for it.
Instead of going even quieter he gets imperious, and then Ed says he's pathetic, and Cameron says he's a nothing and a nobody, and Ed suggests the Chancellor is a "poisonous fungus" and we watchers feel our admiration for them both seeping away a little.
Both sides need to invest heavily in the new generation of barbs, shafts and slashing jokes. The ones they've got are in the antique tradition started by William Hague – and all of them yesterday looked a little prefabricated. "It's no good Wallace asking Gromit," Cameron said, indicating the shadow Chancellor. Hm. Yes. Well. Maybe he's spending too much time running the country.
He went on to say Miliband was "a nothing man at the Treasury and is a nothing man now that he is trying to run the Labour Party".
Labour is perfectly willing to admire the light-touch Cameron. That's a valuable resource for the Tories. It's very undermining for the Labour leader to know his own side is falling for the charm and grace of a superior combatant. Far more than pre-cooked, warmed-up insults.
The arguments he deployed sounded perfectly all right to the casual ear. Why were the banks getting a tax cut? They were paying more tax. Why hadn't the Coalition done more in the last eight months? Why hadn't Labour done more in the previous 10 years? Why were bonuses back at pre-remorse levels? Because that was the contract Labour had written for the bailout.
Tony Blair completely subverted William Hague, remember, by suddenly refusing to play the game of mutual abuse. One PMQs, he came in under Hague's defences with the quiet, reasonable, untheatrical manner and Hague was never really taken seriously in opposition again.
Ed Miliband looks and acts peculiarly enough to be thought of as his own worst critic. The Prime Minister, from the great height of his office, only needs to respond softly, reasonably, pleasantly, to be so annoying that his opponent might burst into tears. That is the goal, after all.