Meet Tatiana and Krista Hogan, a set of 2-year-old twins conjoined at the head. Like most conjoined twins, they share bone, veins and arteries, and in this sense, they share a brain. But their mother believes that because they share a thalamus, each girl can actually see and feel what the other is doing. National Geographic follows these little medical marvels to get an intimate look into their lives. Watch the Hogan family attempt to live as normal a life as possible.