"That's to shove in your mouth if you ask me anything I don't want to talk about," asserts the world's most famous equestrian eventer, brandishing a dummy while sitting in her riding gear in the boot of her brother Pete's Land Rover. The dummy is more commonly sucked by her baby niece Isla who, thanks to the extra Y chromosome between her and Her Majesty, is one place higher in the line of succession.
Not that it matters. The 14th in line to the throne is here to talk about horses, and that's it. Not jubilees, not Granny, and not her rugby-playing husband either.
The day after the opening ceremony, Zara Phillips, aged 31 and now formally but not commonly known as Mrs Tindall, will compete in her first Olympics. It has been a long time coming for the 2006 world champion. Injuries to her horse, Toytown, kept her out of both the Athens and Beijing Games.
"That's just one of the perils of the sport," she says matter-of-factly (she says everything matter-of-factly). "I'm very lucky I had Toytown; I won European and World Championships with him. But there's two of us; you need to get both of us there. I'm not the first person it's happened to. "
At the London Games Phillips will be riding High Kingdom, but it is Toytown, who retired last year, who is still regularly trotted out for the media. It was he, with his distinctive white markings, that she rode through Cheltenham races with the Olympic flame, and it is Toytown she was sat astride prior to our interview at Windsor Great Park, being photographed by the world's press clutching her sponsor's latest smartphone. Taking calls on horseback five weeks before the Games might not be altogether wise, given her previous bad luck, but it's a pretty sedentary affair. Her other commitment is to walk half a mile up and back a grassy stretch of the park, making small talk with a dozen 15-year-old girls from the local school. Even some of the kids seem to find it awkward.
The mile they have walked requires Samsung to donate £1 to charity. The company hopes to raise a quarter of a million - about one four-hundredth of what they have paid to have their logo splashed across the Games and their top executives running with the Olympic torch. Phillips doesn't like the extra attention she gets, but she tries to hide it.
"The focus on me is not an issue," she says. "The other guys in the team know me very well. Hopefully, all the attention we get we can use for the good of the team. I don't think we're the favourites going in. We need to try and get the best out of each other that we can; the best out of our horses. Hopefully, we can use the home turf, and the home crowds, to our advantage.
"We've had the European Championships at Blenheim Palace before, which was home turf. The crowd was amazing, and it was an incredible experience to ride there. I'm hoping everyone will get behind the British team and do the same again."
The equestrian events will be at Greenwich Park, with an extraordinary view over the city and the skyscrapers of Canary Wharf certain to become one of the Games' most iconic images. Tickets have been among the most sought after of all.
"The competition will be difficult because of the terrain, where the course is and where it's set out. It's set in a very small area so it'll be interesting to see what they do with the fences," Phillips explains. "When you come over the hill and you see the city in the background, it is an awesome backdrop, but at the end of the day it's a competition and we need to get on and do what we've got to do."
Competing athletes are given two tickets as standard for friends and family, though Zara's gang might just be able to blag a few extra. Her parents, both former Olympians, won't need one. Her mother, Princess Anne, is a member of the International Olympic Committee; having ridden at Montreal in 1976 she is, for a few weeks at least, the only member of the Royal Family to have competed in an Olympics. Zara's father, Captain Mark Phillips, won gold at Munich in 1972 and will be in London coaching the American team. Zara is not sure – or perhaps won't say – who is coming to watch her, but "Pete will definitely be there".
Her Olympic family have not been as much use as one might think. "Mum unfortunately had a fall when she went to the Olympics; she bumped her head and only remembers the dressage, so I'm not sure what she'd have to say. My father's coaching the American team so I think of him more as the competition right now, but my family are very supportive. I'm very lucky in that way. I probably would never have got on a horse had it not been for them and it's great that they can come and watch."
With her competition beginning on the first Saturday of the Games, Phillips will not attend the opening ceremony, but she is staying in the athletes' village, a rarity for equestrian eventers, whose Olympic arenas tend to be away from the host city.
"I don't know what to expect," she says. "It'll be great to be a part of it."
Zara Phillips is a member of Team Samsung and is supporting Samsung's Olympic Games charity initiative, the Samsung Hope Relay.