Defence secretary Liam Fox today accused his shadow Jim Murphy of "sad and cynical opportunism".
It was in response to an urgent question asked by the shadow defence secretary, following the news that 11,000 armed forces redundancies are to be made by the Ministry of Defence.
If I was Jim Murphy, I wouldn't be too upset about Fox's criticism. A strong opposition has to be opportunistic at times. Since becoming defence secretary, Jim Murphy has proven excellent at exposing flaws or gaps in the MoD and bringing them to the public's attention. Is it opportunistic? Maybe.
Does that make it wrong? No.
It was the second time in recent weeks that Murphy has forced Liam Fox to explain himself in the chamber (the first was over the revelation that the army told soldiers they were losing their jobs via email).
At the time, Fox described the emails as "completely unacceptable" and said the army was investigating. Today, he contradicted himself, dismissing Murphy's urgent question on email sacking alongside "other peripheral issues".
As I wrote in my recent profile of Jim Murphy here, he is one of the most effective operators on the shadow frontbench.
He understands the value of being a strong opposition spokesman – and he occasionally succeeds in getting under the defence secretary's skin, as any good shadow should.
Opposition isn't all about having the space to think. It isn't just about a fresh start for Labour.
It's also about landing blows and attacking the coalition government. It isn't pretty politics. But it's pretty important.