There exists a rare neurological condition, alien hand syndrome that makes one hand of a person act of its own accord.
The hand grasps objects or moves by itself, even if the person doesn’t want it.
This happens due to severe brain injuries when the corpus callosum is severed, damaging the ability to control the movement of a certain limb.
Slowly, your left hand eases up, wraps around your neck and you awake to find your own hand locked in a kung-fu grip on your throat. You pry it loose with your other hand, finger by finger, until it relents and you’re left there staring at a hand that suddenly doesn’t feel like your own.