A far from faultless royal appointment in The Audience, but Helen Mirren is still majestic

Plus: Stoker restores one's faith in film and the National Gallery's Barocci exhibition has a masterpiece that really nails it

Family ties: Nicole Kidman and Matthew Goode star in Park Chan-wook's psychological thriller 'Stoker'

Reading one of the reviews of Helen Mirren's performance in The Audience, Peter Morgan's tableau vivant about the relationship between the Queen and some of the 12 Prime Ministers who have come and gone during her reign, I was particularly struck by one word – "faultless". It seemed an odd word to use, not because Mirren wasn't good in the role, but because faultless was precisely what she wasn't. Possibly the critic in question didn't go on the same night as I did. But if he did then this looked like an interesting example of regal aura. Because what was notable on the first night was that Mirren was still a bit rocky on some of her lines. There were a few uncharacteristic stumbles, the odd moment when there was a little rattle to the rhythm as she struggled not to derail entirely.

Perhaps, I thought, her performance was "faultless" in the same way that the Queen's complexion is always described as "flawless". That is, it's not strictly true (to be faultless and flawless is not to be human) but it's a way for a loyal subject to pay obeisance.

That critic may, perfectly legitimately, have thought that the odd stumble over a word or two was irrelevant to the larger picture. But such things are never irrelevant to the audience, or to the performers themselves, I would have thought. By coincidence, I noticed that James McAvoy had touched on the subject in an interview about his critically admired performance as Macbeth at the Trafalgar Studios. He'd caught himself saying the same line twice, he confessed, "and I went 'Oh dear this is a bad moment for me'."

Rather touchingly, he then added that he thought the audience "didn't quite notice", which was reminiscent of Mrs Overall in Acorn Antiques, insisting that the viewers probably wouldn't spot that she'd arrived on set carrying a completely imaginary tea tray. I have news for Mr McAvoy. The audience will have noticed but they will have been as eager as you were to pretend that it didn't happen.

That's because these are always moments that strike a deep anxiety into us. On paper you might think that we've nothing to lose, being hidden in the darkness of the auditorium. Or that what we've got to lose is purely a matter of value for money, a contractual failure to deliver (rather literally). But the truth is that they illuminate the peculiar intimacy between a performer and his or her audience and the odd way that the possibility of a fall is what makes the theatrical experience work. It's jarring, of course, to find your suspended disbelief thumping to floor. At one moment, Mirren is Her Majesty; at the very next, she's a famous person pretending to be Her Majesty and caught, moreover, at a moment when the pretence has been exposed.

What we feel for her as an actress (and audiences are never less than sympathetic) intersects with what we're supposed to be feeling for the character she's playing and it can take some time to restore normal service. It's not just the performer who has to get it "back on track", as McAvoy put it. It's us too.

Maybe "faultless" was right after all though. Because there's an odd quality to these stumbles, when they come from seriously good performers, which only enhances the pleasure of everything around them. A mediocre actor can't afford the luxury, because every stammer or hesitation only confirms the sense of a failing endeavour. But with a good actor it simply highlights what's usually invisible – the fact that you have been hypnotised into forgetting the artifice.

Like a beauty spot on a perfectly proportioned face, it isn't a blemish that makes appreciation impossible. It's one that emphasises and magnifies it. The only problem is pedantry, which won't allow the term through. Perfectly flawed, perhaps. That gets a bit closer to it.

Stoker restores one's faith in film

A while ago Ian McEwan wrote about his occasional losses of faith in fiction which, in his case, were generally cured by an encounter with excellence. It happens in other art forms too. You can go along for weeks in the theatre or the cinema not really emotionally stirred by it until suddenly you're reminded why it can thrill. It has happened twice to me recently – once when watching Ron Cook utter the word "Kean" in Trelawny of the Wells, and several times while watching Stoker (above), Park Chan-wook's psychological thriller. I can recommend either to those of enervated aesthetic sensibilities looking for a restorative pick-me-up.

A masterpiece that really nails it

Details can matter a great deal in art too. If I'm honest, I wasn't hugely moved by the National Gallery's Barocci exhibition, fine though it is as an example of the curator's art. The paintings are just too pious for me. One thing did punch through though, with an almost physical impact. It's in the foreground to an altarpiece depicting the Entombment of Christ, and it consists of the tools that have been used to get him down, alongside some bloody nails and the crown of thorns. I must have seen hundreds of Depositions over the years, given the popularity of this subject, but I don't think I've ever seen one that so forcefully confronts you with the horror involved in getting Christ off the cross. Where would you find a leverage to get the nails out again?