Krista and Tatiana Hogan can do things that nobody else can do.
They share the senses of touch and taste and can control one another’s limbs.
Tatiana can see out of both of Krista’s eyes, and Krista can see out of one of Tatiana’s. Tatiana controls three arms and a leg, and Krista controls three legs and an arm.
They have different personalities - one of the girl's is very confident, while the other is a very gentle soul. But what they share is something no one else in the world has ever experienced.
Mamamia's Jessie and Clare Stephens talk twins. Post continues after podcast.
Krista and Tatiana are craniopagus twins, which means they are joined at the head. Their brains are connected by a thalamic bridge, which acts like a switchboard relaying sensory and motor signals and regulating consciousness. This means that their two separate brains can behave as one.
"They can sit there and not say anything to eachother, and all of a sudden one of them will pop up and grab something to eat for the other one. Like, there's no words being spoken between the two of them at all, and they know exactly what the other one wants," their mother Felicia Simms told 60 Minutes Australia in 2012.
"You can tickle one, and the other one laughs. You pinch one, the other one will cry with her like she's feeling it," she added.
While speaking to CBS, Felicia explained that it "actually takes a lot more effort for them to see things through eachother than feel things". And the girls can decide when they'd like to control the other twin's movement, or taste what they're tasting.
Krista and Tatiana were born on October 25, 2006, in Canada and are now teenagers. Their mother was just 21-years-old when she gave birth. The twins have an older brother and sister, and went on to have a younger sibling rounding out their family of seven.
It took 16 medics to deliver them safely into the world, with the twins given just a 20 per cent chance of survival. A CT scan has shown they can never be separated due to the risk of serious injury or death. They each have their own organs, but their vascular system works as one with their blood pumping through one girl into the other.
The girls are diabetic and have epilepsy, take a regimen of pills, and need frequent blood tests. But they are able to go to school for a few hours a day, and they love swimming, camping and video games.
"They're just little people that are here living their lives like the rest of us," Felicia told the documentary Inseparable: Ten Years Joined At The Head in 2017. "That's how we see them and that's how their siblings see them."
The documentary followed the girl's lives for a year leading up to their 10th birthday party. But their mother said at the time it would be the last documentary about the twins "for now".
"Now that they're 11 they can decide for themselves how much to share with the world," she said.
Watch: The twins and their mother shared their story with various media during their younger years. Post continues after video.
The twins have, as far as Mamamia can determine, decided to do just that. Share their world with just eachother and their loved ones for now - with no articles, documentaries or photos of the girls easily available online from their teenage years.
During the 2017 documentary the girls shared that when they were little, they used to try to "pull their heads apart". Their mother, however, always told them they were stuck, "so they would have to work things out".
They still argue as most siblings do of course, admitting that "some days they don't like being together".
Over the years, Tatiana has become the more prominent leader between the twins. When she was younger she described herself as being "the red Power Ranger," aka, the leader - Jason.
"Krista is quieter and can be more in her own shell," their mother explained.
Neurosurgeon Dr Douglas Cochrane who has followed the girl's progress since they were born, says the only other twins he knows of who had this form of joining, though not the bridge, were two Iranian sisters. The girls chose to have surgery as they neared adulthood to attempt a separation, but didn't survive.
It's a comment that's made to the girls and their family by complete strangers often.
"People’s immediate response is, 'The twins should be separated—let’s make them like us'," Dr Cochrane told Vancouver Magazine.
As Krista and Tatiana Hogan's family have explained over the years in various documentaries, the girls will remain as they are.
Communicating and living their lives connected in a way that continues to baffle medical experts.
"There’s nobody in the world that’s connected the same way that they are," their mother said in 2017. "I could have never imagined that they could do anything they can do now."
Feature image: Channel 5.