The Minister for Transport was discussing the issue of "modal shift".
Answering Dáil questions about traffic, he endorsed Opposition suggestions that modal shift was something to be desired.
"Getting people out of their cars and into public transport is something I agree with," he said.
Oddly enough, this is exactly what the Opposition had in mind for Mr Brennan.
As the (until yesterday) unnamed subject of allegations about a minister and an unpaid €5,000 bill for alcohol and cigars, he seemed a prime candidate for a bit of modal shifting himself. And the word in Leinster House was that if Mr Brennan needed any encouragement to get out of his State car, the Opposition would be only too pleased to help.
Rarely has a Government bill excited such interest in the Dáil as the one allegedly run up with Aer Rianta by a Government minister in the 1990s.
Deputies not normally known for their love of legislation were looking forward to publication of the bill yesterday, followed by a second and third reading, and maybe a fourth and fifth reading too.
None of it happened. Indeed, throughout Mr Brennan's question time, there was no reference to the issue.
And the phoney war continued into leader's questions, when Fine Gael leader Enda Kenny referred to allegations about an unnamed minister.
But even when Mr Ahern finally confirmed the "big news" that Mr Brennan (beside him and smiling wryly) was the man at the centre of the storm, he immediately stymied the resignation calls by reading Mr Brennan's statement of denial.
In the event, the nearest we got to details about the bill was the Taoiseach's appeal for sufficient time for the matter to be properly investigated.
There were many variables in the original newspaper story, he said, so there was no point in him just dismissing the allegations at this stage as "a puff of smoke".
Indeed. At early 1990s prices, the equivalent of €5,000 would have bought a lot of smoke, even the top-of-the-range Cuban variety.
And as for the whiskey and brandy, Mr Kenny calculated that the bill would have accounted for 250 bottles.
"A hell of a Christmas party," he suggested.
Apart from such speculation, the Opposition was inclined to take Mr Brennan's statement at face value and await the outcome of the promised inquiry.
Labour's Pat Rabbitte was troubled, however. If the Minister had no memory of the alleged bill, why had it taken him more than two days to say so?
If a Minister for the Arts had been accused of taking items "out of the National Gallery", he would know immediately whether he'd done it or not, reasoned the Labour leader.
The Taoiseach appeared to agree. Reckoning that the value of the goods involved could be nearer to €12,000 in today's values, he expressed the hope that his Cabinet colleagues "would remember if they drank that. . . particularly if it was in one Christmas".
Maybe they'd remember drinking it; maybe not. But they'd surely remember the hangover.