Cut the Corpus Callosum in the Left and Right Hemispheres

In a bird, it's quite obvious that the two are very separate and they're doing separate things in humans. It's much less obvious until you do something drastic, like cut the fibers that connect the left and the right hemisphere. And this was done historically by surgeons to stop epileptic seizures. When they did that, initially people thought, Oh, these guys are fine. Like you don't even need the corpus callosum. But when they looked closer and more subtly, what they found was almost like there were two independent conscious entities living in each person.