A person walks clumsily after consuming alcohol primarily because alcohol affects the cerebellum, the part of the brain responsible for coordinating movement, balance, and posture. Here are the key reasons:

1. Cerebellar impairment: Alcohol slows down the activity of neurons in the cerebellum, disrupting its ability to coordinate fine motor movements, leading to poor balance and clumsy walking, a condition known as ataxia.
2. Slowed reaction times: Alcohol impairs the brain’s communication pathways, reducing the speed at which signals are transmitted between the brain and muscles. This delay in response results in uncoordinated or jerky movements.
3. Impaired judgment and motor control: Alcohol affects the frontal lobe of the brain, which is involved in planning and controlling movement. This leads to difficulty in judging distances and regulating walking patterns, contributing to unsteady movement.

Together, these effects of alcohol on the cerebellum, motor control, and reaction times make walking difficult and unsteady after alcohol consumption.