Microcosm/macrocosm.

Wasn't there a character in Stanley Kubrick's Dr. Strangelove, that had a hand with a mind of its own?

Since the 1940s, neurosurgeons have been performing corpus callosotomy—a surgery that serves as a last resort for treating epilepsy. It included cutting through the corpus callosum, which functions as the main connection between the two hemispheres of the brain. The procedure was considered dangerous by some and less preferred by many, yet it relieved most patients from unbearable epileptic seizures.

Corpus callosotomy “keeps the electrical signals that cause a seizure from crossing over and wreaking havoc,” says Emily Temple-Wood, Wikipedia editor and medical student who was named the Wikipedian of the Year in 2016. “It’s amazing how well these patients adapt and recover, and this is all due to how plastic the brain is.”

Studying those patients helped neuroscientists make sense of how the two halves of the brain work together, what are the functions of each of them and what would happen if they worked separately. In the last mentioned case, the brain behaved as if there were two separate minds, or what they called later split-brain. Wikipedia tells us about it that:

After the right and left brain are separated, each hemisphere will have its own separate perception, concepts, and impulses to act. Having two “brains” in one body can create some interesting dilemmas. When one split-brain patient dressed himself, he sometimes pulled his pants up with one hand (that side of his brain wanted to get dressed) and down with the other (this side didn’t). Also, once he grabbed his wife with his left hand and shook her violently, so his right hand came to her aid and grabbed the aggressive left hand. However, such conflicts are actually rare. If a conflict arises, one hemisphere usually overrides the other.

https://diff.wikimedia.org/2017/09/14/wait-what-split-brain/