Why should you not touch the horn or connecting pipe when using a carbon dioxide extinguisher?

You should not touch the horn or connecting pipe of a carbon dioxide extinguisher because they can become extremely cold during operation due to the rapid expansion of CO2 gas. This can cause frostbite or skin damage upon contact. Additionally, the horn can discharge CO2 at high velocity, posing a risk of injury if mishandled. Always handle the extinguisher by its body and use the handle to aim the nozzle safely.