Meet the asymmetrical 'mirror-image' twins
Meet the asymmetrical 'mirror-image' twins who do everything from parting their hair to holding a pen - in precisely OPPOSITE ways.
Leah and Erin Sullivan, four, are like "two sides of the same coin" according to their mum Zoe, 42.
Leah parts her hair on the left, and Erin on the right and they favour opposite hands for throwing or writing.
The pair even sleep in exactly the same position - but on different sides.
They are 'mirror-image twins' - a little-known phenomenon that means otherwise identical siblings are asymmetrical in their looks and how they move or interact.
The phenomenon is believed to affect up to a quarter of identical twins, and Zoe found out her twins were affected last year
Stay-at-home mum Zoe, from Inverness, Scotland, said: "If there hair has been up it's really hard to tell them apart!
"Leah's hair grew faster, but it wasn't until they were both about two and a half that their fringes started to grow out and I realised it parted on different sides!
"It didn't matter what you did, like trying to part it in the middle or on the other side, and really it's the only way you can tell them apart!
"That is when we realised they were mirror twins.
"Erin we think could be left-handed but Leah is definitely right handed.
"After I noticed it I did look it up on the internet, it can be really extreme!"
Their nursery also uses their unique hairstyles to tell the difference, but there could yet be more symmetries that reveal themselves as the girls grow older.
Zoe added: "They are totally different in personality.
"Almost like different sides of the same coin. Every bit of personality Leah has, Erin doesn't, and vice versa.
"Erin is very much straight down the line - what you see is what you get - but Leah is more cheeky and the total opposite!
"You see quite a lot of twins that are similar personality-wise but with them it is like one person split into two.
"Leah's got a really good sense of humour but Erin doesn't quite get it - she's a lot more serious."
Identical twins are the result of a single fertilised egg splitting into two embryos between four and eight days post-conception.
It is thought that mirror twins are the result of the egg splitting even later, between nine and 12 days, although this has never been proven.
Mum-of-eleven Zoe said: "Twins do run in the family on my side, as my grandad was a twin and I have twin aunties, but they were still a bit of a shock!
"I also already had a pair of non-identical twins four years before, and I think part of me knew deep down that they were going to be twins, but I was more shocked they were going to be identical."
The girls were born prematurely at 27 weeks on January 25 2016, on the eighth birthday of her first set of twins.
Leah weighed 3lb 4oz and Erin 2lb 6oz at birth, and were hospitalized for six and 10 weeks respectively.
Leah suffered a collapsed lung, Erin contracted sepsis and had extra fluid in her brain, and both girls had heart murmurs.
At one point Erin only weighed 810g, and with seven other kids at home at the time, both parents were exhausted.
Zoe, who is married to the girls' dad Ben, said: "It was a very traumatic time.
"Ben was doing half days so could look after the other children whilst I was in the hospital and then we would swap- I have no idea how we did it!"
Zoe admits that when they were babies it was almost impossible to tell the girls apart.
Mum Zoe said Leah usually stands on the left in photos, with Erin on the right, and they walk with opposite dominant feet.
And when they face each other it looks exactly like they are looking in the mirror.
