Their condition is rare in and of itself – Krista and Tatiana Hogan are conjoined twins – but it’s where they are conjoined that amazes people.

The twin girls, who are 4 years old, were born with craniopagus, meaning they were fused at the skull. And these girls have shocked doctors – they literally share one mind, meaning they can hear each other’s thoughts and see through each other’s eyes, The New York Times reported.

Krista and Tatiana, who live in Vernon, British Columbia, share the part of the brain called the thalamus.

If one girl is drinking or eating too much, the other will feel full.

“It’s like they are one and two people at the same time,” Todd Feinberg, a professor of psychiatry and neurology at Albert Einstein College of Medicine in New York City, told the Times.

Only 1 in 2.5 million pairs of twins are born with this condition, and only a small number survive.

Doctors told the twins’ parents Felicia Simms and Brendan Hogan that it could be “potentially lethal” to separate the girls.

They are developmentally delayed, but happy children, who live with their mother, siblings and extended family.

Click here to read more about this story from The New York Times.

Click here to see a slideshow of other conjoined twins.