One bit of probing in the wrong place and it could have all gone wrong, potentially leading to incomprehensible outbursts in Greek, or even Latin.
This head case aimed to discover how the former Prime Minister thinks, what he honestly believed, what he believed he believed when he said he believed it, and how closely connected is that which comes out of his mouth to the mysterious workings of his cerebral cortex.
Throughout his political life Mr Johnson's opponents, who include many Conservative MPs past and present who have always disliked him, have characterised him as an untrustworthy liar and scoundrel, living in a fantasy world, a delusional political outsider in touch with neither reality nor the truth.
So here is an underlying paradox for the privileges committee which grilled him this week. If all that is true – that is, that he is a delusional political outsider in touch with neither reality nor the truth – how can he be found guilty of deliberately and intentionally misleading the House of Commons?
Boris Johnson's response to the accusations partly boiled down to the Kenneth Williams defence – infamy, infamy, you've all got it in for me.
Then there was the gambit that if the committee was saying he was a liar, it was also accusing all the civil servants and advisers who thought the parties complied with the guidance of being liars as well.
In other words, if we are all guilty, we are all innocent. Not that they were parties in the first place. They were allowable work events at which he displayed admirable leadership by popping in to raise the morale of the hard-pressed staff at a time of national crisis.
But yes, he admitted, 10 Downing Street was guilty. By that he meant the building itself which, as everybody knows, is so small that social distancing is not always possible.
"Downing Street is a cramped, narrow, 18th century townhouse," said Boris.
"We gave each other as wide a berth as we could."
It turns out he didn't even get to eat that famous Union Jack birthday cake. According to his evidence, an aide ate it.
With the departure of Boris Johnson from high office we are all supposed now to be in a new era of trust in politicians, in which case you may not find anything odd about politicians sitting in judgment in relation to the honesty and straightforwardness of other politicians.
MPs are required to swear allegiance to the Crown. They are not required to swear to the tell the truth.
At the start of his evidence Boris Johnson swore on the holy book to tell the truth, the whole truth, and nothing but the truth. What a great idea. But it will never catch on. For a start politicians, for the sake of party unity, have to pretend to support party policies which they may actually disagree with.
The privileges committee will now have to digest the former Prime Minister's evidence and decide if he deliberately misled the House.
So far as I can tell the general expectation seems to be that it will conclude he did.
But there is another possibility, that he is exonerated, being found to be afflicted by Boris Johnson Syndrome.
It had to happen some time. Earlier this week I was told about a woman whose daughter self-identifies as a cat.
And as a consequence she eats cat food.
For some reason this stirred me into the realms of poetry.
There was a young woman who self-identified as a cat,
Fancy that, she thinks she's a cat.
It's worried her mum and upset her sisters,
Because they'll all go hungry when they run out of Whiskas.
Which reminds me of an old joke.
"Doctor, doctor, my wife thinks she's a hen." Doctor: "Don't worry, I can cure her." "Oh, please don't do that." Doctor: "Why not?" "We need the eggs."
Oh, and by the way, at the risk of boring you with my oft-repeated contention that economic forecasting is at the disreputable end of the astrology spectrum, inflation rose "unexpectedly" to 10.4 per cent in February.