Many things in nature are inexplicable, including our physical structure and illnesses in the body. Sometimes, even doctors can't tell the reasons but maybe these are challenges in life to train us tougher.

Tatiana and Krista Hogan are Canadian craniopagus twins whose head are fused together. 

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According to CBC documentary, the twins were expected to live less 24 hours after they had been born, but lives are tougher than anyone expected. They just celebrated their 11th birthday in October and they've learnt to swim.

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Krista and Tatiana are one in 2.5 million. Their heads are conjoined and it allows them to understand each other without saying it out. They can see through each other's eyes and taste what each other eats. 

"The abilities they have that no one else could imagine having are just incredible," their parent Hogan said.

Even suffering from Type 1 diabetes, they go to school in Vernon, B.C. for a few hours every day. 

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"For them to actually be here for 10 years is just a blessing," said Hogan in an interview with the media. "It just felt so good to see them get to this milestone."

Except for the twins, the parent are raising other three kids 15-year-old Rosa, 13-year-old Christopher, and 9-year-old Shaylee.

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Krista and Tatiana's doctor, pediatric neurologist Dr. Juliette Hukin, has followed their case since they were two, saying "they're the only twins that I'm aware of who are alive and remain conjoined with this shared connectivity."

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Even with the connected body, they have definitely different personalities. Dr. Juliette said they can now better understand their connection. 

Krista loves playing pranks and making people laugh. She is also the bigger sister who tends to take charge, Hogan explained. Meanwhile, Tatiana is a "little lovebug." She is a loving kid. She cuddles animals and wants to hug everyone who comes by the house.

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"They're just little people that are here living their lives like the rest of us," Hogan said. "That's how we see them and that's how their siblings see them."