It cannot be the rejuvenating effects of the five Oscar nominations for the writer-director's new film, Her, or his Golden Globe for best screenplay, because when we meet those lie in the future. Maybe he is still jazzed from his latest appearance front of the camera in The Wolf Of Wall Street. Or perhaps it is the nap ("22 minutes") he has just enjoyed. Whatever, he is in a playful mood when we meet in London.
"See that guy over there?" he says, pointing at the building opposite where an office worker is engrossed in a newspaper. "What paper is he is reading? Wouldn't it be funny if that was your paper?"
It would certainly be a very Jonze moment, a bolt from the blue-skies mind responsible for Being John Malkovich, Adaptation (both with Charlie Kaufman), Where The Wild Things Are, and many a music video, commercial and Jackass prank in between.
Her, Jonze's first feature film since bringing Maurice Sendak's Where The Wild Things Are to the screen in 2009, is causing quite the wild rumpus. There are those Oscar nominations for a start, confirmation in many minds that this romantic drama about a writer (Joaquin Phoenix) who falls in love with a computer operating system (voiced by Scarlett Johansson), is his best picture since Being John Malkovich. While technology necessarily features in Her, the story is an old-fashioned one of two strangers getting to know each other and changing, for good or ill, in the process. As Jonze puts it: "We want to be known, but at the same time, are afraid of being known."
A large part of the picture is spent with the camera on Phoenix's face as he reacts to Samantha's voice. (Samantha Morton originally played the part on set. "Even though she is not in the movie any more," says Jonze of the British actress, "she still kind of is because her DNA is in his performance".)
One might leave Her with the notion that the familiarity bred by love carries risks of its own, but Jonze (real name Adam Spiegel) says he is not out to send a message about anything. "I want to make a movie that people can have their own personal reaction to. Whatever your reaction is, is perfect. That's what I aspire to, those are the movies I like the best. Movies that every five years I'll watch again and have a different reaction to because I'm different."
Harold And Maude is one such film for Jonze. 2001: A Space Odyssey is another, largely for what Kubrick leaves out. "To be that confident and that virtuoso a filmmaker, and to leave the narrative that much in the imagination of the viewer, is so bold. That's really inspiring."
"Bold" is not a word often applied to the movie business of today. So much money goes into movies up front that backers want to be assured of returns before a scene shoots. That would seem to be the antithesis of the way Jonze likes to work.
"We've been really lucky," he says of the creative team he has been with since the early days. "Our movies don't cost a lot of money." Where The Wild Things Are was different. It had a major studio behind it, bucks were spent. The website Box Office Mojo puts the production budget at $100 million, and estimates the picture made just over that worldwide. Being edgy and dark in places, this was not a traditional family film - in the same way that Sendak's 1963 classic was not a traditional children's book.
"That was hard and we fought a lot with them. Ultimately they are scared because they are responsible for an amount of money, they are responsible to their shareholders, their bosses, they're scared of getting fired or looking bad in the community. But when it comes down to it they can't possibly care as much about their jobs or looking bad in their community as I care about my movie. I don't … I will … you know … I will, uh, I will never stop."
That last sentence, with its mix of hesitancy and pluck, sums up Jonze. In person he can be very reserved, happiest when talking about others, bolting at the least sign of a personal question like a rabbit catching the scent of a hunter.
At the same time, there is a determination to do things his way. That was probably the reason he clicked so well with Sendak, who paid him the ultimate Sendakian compliment by calling him a throwback to a 1960s kid, "kind of crazy but in the most wonderful, adventurous way".
"It was his unwavering truth in everything he did and said," says Jonze when I ask what he remembers most of Sendak. "He had no interest in wasting time with small talk, or worrying about people liking him, trying to get people to like him. He didn't give a **** in the most amazing way. He was going to be who he was going to be in every aspect of what he did, whether it was dealing with business, dealing with people in his personal life, or dealing with his art. He was at that place."
There's a similar "life's too short" philosophy running through Her, which also stars Amy Adams as Theodore's best friend and Rooney Mara as his ex. Is that something he has adopted? The nose twitches and he's off on another list of names, but he eventually arrives at an answer.
"It's certainly something I admired in Maurice. It's something I admire in all my favourite artists. Charlie Kaufman is that way." The rapper Kanye West and Phoenix are the same, he adds. Being yourself is really all you can do, I say. "It's hard though, the battle between being truthful and being liked."
Jonze in many senses has come a long way from the kid who made music videos for a living. They were his film school, though he doesn't want to put it like that because it sounds like it was a means to get to somewhere rather than a worthwhile destination in itself. He certainly had some star fellow pupils, with directors David Fincher, Michel Gondry and Mark Romanek in the same building. They would borrow art books from each other (Romanek had the best collection).
Jonze is still heavily involved in music, putting together the recent YouTube Music Awards. Then there is his Jackass side, where he gets to indulge his boyhood dream of being a stuntman. What Malkovich fans will want to know is if there is any chance of Jonze and Kaufman reuniting. "We always talk … We have a lot of ideas. We share so many common tastes that I would imagine we would. I don't know when because I'm focused on writing my own things and he's focused on writing his own things."
You can currently see Jonze on screen in The Wolf Of Wall Street, where he plays a small-time share dealer. He was only on set for a day, but it could have been five minutes and he would still have jumped at the chance of seeing Martin Scorsese work. "He can do anything. He is like a jazz maestro. He knows all the rules so he can break them all."
Her is remarkable for its script and performances, but there is another reason why it might cause a rumpus. Some could see the story of a broken-hearted creative type learning to love again as close to Jonze's own experiences. Once married to Sofia Coppola (they divorced in 2003), her film, Lost In Translation, the tale of a wife hanging around while her busy-busy husband is off working, was rumoured to be drawn from their life, though Coppola has rubbished the idea.
I ask Jonze if there was anything in Her that relates to his personal circumstances or if it was entirely fictional.
"It's a combination of things I feel and then my imagination, taking something I might feel in a relationship," he says. "But it's not so much like a one to one where I'm Theodore. I wrote myself into all the characters, I relate to all the characters. That's maybe the key to making sure you don't write a one-sided movie."
Just one side to Spike Jonze? No chance.
Her opens in cinemas on February 14