Why do you sometimes get a shock when touching a metal object after walking on carpet?

Answer: A voltage difference drives a brief flow of charge between you and the metal

A voltage difference drives a brief flow of charge between you and the metal ✓ — A voltage difference between your body and the metal can drive a brief discharge that you feel as a shock. Contact and separation between shoes and carpet can leave your body with excess or missing electrons. Electrons may flow into or out of your body, depending on the charge imbalance; they do not always flow from you into the metal.

A chemical reaction between your skin and the metal creates a small electric current — The shock described here comes from a rapid discharge, not a new chemical reaction between skin and metal. Contact between shoes and carpet can separate charge before you reach the object. Touching a conductor then lets charge redistribute rapidly, producing the brief sensation.

The metal supplies a continuous electric current, like a battery — An unpowered metal object is not a battery supplying a continuous current. Here, an existing voltage difference drives a brief redistribution of charge, and the current stops as that difference falls. Metal provides a conductive path; it does not continuously create the charge.