Which of the following is considered a mild symptom of poisoning?

In the context of poisoning symptoms, dizziness is often categorized as a mild reaction. It can occur due to various factors, including the type of poisonous substance ingested or inhaled. Dizziness may result from the body's response to toxins, causing a temporary disturbance in balance and equilibrium.

The other symptoms listed are usually associated with more severe reactions to poisoning. For instance, contracted pupils, muscle twitching, and difficulty breathing typically indicate more serious issues that require immediate medical attention. These symptoms can signify central nervous system involvement or respiratory distress, which are conditions that may necessitate urgent intervention. Therefore, dizziness, while concerning, is often seen as less severe compared to the other symptoms mentioned, making it the correct choice for a mild symptom of poisoning.