Numbers, of course, are the ammunition of politics and Red Ed and Blue Dave were firing them off at speed, leaving the onlooker's head spinning.
The subject on this occasion was the dear old NHS.
Now when the chief comrade asks a question that relies on statistics you know a) he already knows the answer and b) he expects the PM not to give it.
So we went from cancer waiting times to A&E with Red Ed claiming the figures showed things were getting worse while Blue Dave insisted, actually, things were getting better.
The Tory chief quoted the shadow health secretary quoting the Commonwealth Report, which said England had the best health service in the world. "It's official!" declared Dave to Tory cheers.
Edjumped up to insist it was Labour which created the NHS in the and "every time we have to save it from that lot opposite". The comrades cheered.
After their chief lobbed another statistical hand-grenade at the PM, Flashman used his default weapon, accusing Labour of being responsible for the horrible Mid-Staffs scandal.
When Red Ed delivered yet another statistic, Blue Dave said: "Honestly, if he can't do better than that, even on the NHS, he really is in trouble."
The PM was on a roll and couldn't pass up on some little local difficulty, noting how Labour's policy chief Jon Cruddas had at the weekend complained there were "no interesting ideas" from its policy review and Blue Labour guru, Lord Glasman, suggested Mr M had "absolutely no vision".
He then told Labour MPs: "I would say to the people looking glum behind him - cheer up folks, it's only Wednesday."
Later, Tory backbencher Tony Baldry raised his party's morale by pointing out how in the 1983 election a 13-year-old boy delivered leaflets around his constituency, pledging Michael Foot would take Britain out of the EU. That boy, he noted, was none other than Red Ed.
Blue Dave suggested it was wrong to hold youthful indiscretions against people but if that was his rival's idea of fun, then one had to accept it.
When someone asked what his idea of fun was, the PM snapped: "It is not hanging out with the shadow chancellor.
"I feel sorry for the leader of the opposition because he has to hang out with him all the time.
"What a miserable existence it must be!"
For once, Red Ed looked in total agreement.