"Can I join the Right Honourable Friend in paying tribute to our forces in Afghanistan, who I visited last week..." - watch here at 2m42s.
Minutes later, the pressure again seemed to be getting to Cameron. Perhaps he was rattled by Ed's much better performance this week, for he then managed to refer, twice, to the very clearly female Labour MP Joan Ruddock, as male - "the Honourable gentleman" (13m54s) and "than in his" (13m48s).
I admit (uncomfortably) that Cameron is a very capable Prime Minister (indeed a little bird at No 10 tells me that he is exceptionally professional, courteous to staff and collegiate in letting Ministers take decisions). However, counter-intuitively, the very ease with which he does the job of PM is a potential weakness. There's no doubt that he's an assured performer in PMQs, yet when he's rattled, as he was last week by Ed's 'Bullingdon Club' put-down, his instinctive reaction is to be extremely patronising, verging on nasty. Tony Blair mastered wit and humour at the Despatch Box. He was rarely, if ever, nasty to his opponents. Such a talent served him well. In Cameron's occasional nastiness there is the danger that seeds are being planted in the public mind that he is a little too clever for his own good. Arrogance is not an endearing human attribute and it is one that he is particularly vulnerable to, given his personal background.
Arrogance, added to a sense that he and his senior colleagues are out of touch with ordinary people (including ordinary top tax payers who are to lose what little state benefits they receive) could prove particularly dangerous to the Tories.