Christie and Louise Miller, mirror-image twin sisters who sing under the name Millers Daughter, are telling me about something curious that happened to them the night before we meet – an almost supernatural occurrence that, because it affected one, affected the other, too.
Mirror-image twins are effectively a reflection of one another who share the same DNA but develop asymmetric features, and, like many twins, they speak of sharing an almost psychic connection.
"I woke up in the middle of the night in our hotel room," says Louise, "scared to death. Christie woke at the same time. Then I said, out loud: it's OK, it's just me."
"The same thing happened to us in New York a while ago," says Christie, "only that time it was me saying: it's OK, it's just me."
They have no idea of what, if any, significance this may have. "It's unexplainable," says Louise.
But the unexplainable seems to happen to them rather a lot. They regularly experience visions – ghostly ones, other worldly, and voices from beyond the grave. They see spots of blue light around people from whom they get a "good aura", and they always see them together, at the same time. They don't know why it happens, it just does.
"It's hard to talk about something like this," says Christie, "especially to someone who may not have had similar experiences, because I know how it makes us sound – like nutjobs."
Christie shrugs, Louise shrugs, and then they turn and look at me, their translucent, green eyes unblinking, their smiles unreadable.
The twins are used to bewitching people, they tell me. It's something all twins have to put up with – the endless curiosity of others – but it is something certain sets actually foster, by dressing alike, styling their hair alike, and being rarely, if ever, seen apart.
Christie and Louise are, to all intents and purposes, joined at the hip. They were the sort who, growing up, insisted that their parents buy them the same clothes. They went to school together, and now they sing together. And despite having asymmetrical features, they are all but identical.
The only real discrepancy is that Louise has Crohn's disease, and Christie doesn't. She now struggles to keep weight on, while her sister is fuller figured. It is no longer difficult to tell them apart.
A quarter of all identical twins are reported to be mirror image, which means that there are approximately 2.5 million in the world.
Christie and Louise learned of their mirror-ness only recently. It happened while taking part in a research study at St Thomas' Hospital in London. Dr Kirsten Ward, the European Research Council project manager for the TwinsUK registry at St Thomas', King's College London, tells me that there isn't a test to determine mirror image.
"It's more of a physical appearance thing, but they do share 100 per cent of their DNA," she explains.
In most cases of identical twins, she says, the egg splits between days one and eight after conception. The split in mirror-image cases tends to occur after nine to 12 days.
"So it's a late split, and this seems to promote a kind of asymmetry in them. For example, they might have a different dominant hand, and there are instances where one has their heart on one side of their chest and the other, the other side. Appendixes too; even vein structures in opposing arms. We don't quite know why."
The Millers were told they were very close to being conjoined. The news thrilled them, making them feel, if anything, even closer, "although we always have felt pretty much one mind in two bodies," says Louise, "like basically the same person".
At school, they both took the same exams, and received the same grades. This caused some consternation amongst their teachers, but Nancy Segal, an American psychologist who specialises in twin studies, and is the author of several books on the subject, suggests that this isn't unusual at all.
"They have separate minds, of course, but they do work in very similar ways," she says. "I've actually been an expert witness in cases [in the US] where twins were accused of cheating because people couldn't believe they could produce such identical results. But I fully believe they can. Genetically, they are the same, so they are going to respond to problems and situations – and exams – in the same way."
It is this intrinsic connection that mirror image, and identical, twins can exploit in their professional lives. In the world of tennis, for example, the American doubles champions and mirror twins Mike and Bob Myers are a dominant, often unbeatable, force – their world ranking is No. 1 – because they play like an extension of one another. Similarly, with Millers Daughter and their music. Their album, a breezy, Fleetwood Mac-inspired affair, is as effortless to listen to as it was to record.
"Music has always come very naturally to us," says Louise. "Our ideas are the same, they happen at the same time, the lyrics, too. And playing together is completely instinctive."
But is there a downside to being quite so permanently connected? Being twins, some say, can often resemble a rather exclusive club of two, one that is difficult to permeate. The Millers are 29 years old now, and still live at home in Wiltshire with their parents, where they continue to share a bedroom. It wouldn't make sense, they say, for one of them to move into the spare room. I ask about relationships. What happens then?
"Neither of us is in a relationship at the moment," says Louise.
And when they have had partners in the past – what then? They exchange a loaded look.
"Well, they tend to feel a little pushed out by us, and it can get awkward. I did go on holiday with a boyfriend once, without Christie. It was… weird."
Ms Segal, a twin herself, is often confronted by such speculation, that twins can sometimes live rather repressed social lives but, she says: "Who are we to impose our judgement on what works for them? I would actually suggest theirs is a relationship many people envy, because how great to have someone you trust and accept unconditionally, your best friend, always by your side?"
There are no findings to suggest twins have higher divorce rates among those that marry, and a recent study in Denmark has suggested they are far less likely to commit suicide.
"It's because they have a built-in support system with them all the time," says Ms Segal. "They are never lonely. So maybe there are actually a lot of advantages to being a twin. Maybe they have richer lives than the rest of us."
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