Which of the following is NOT a mild symptom of nerve agent poisoning?

Severe muscular twitching is indeed considered a more serious symptom of nerve agent poisoning, not a mild one. Nerve agents disrupt the normal functioning of the nervous system by inhibiting the enzyme acetylcholinesterase, leading to an accumulation of acetylcholine. This accumulation can cause overstimulation of muscles, resulting in significant muscular twitching and convulsions, which are categorized as severe symptoms. In contrast, symptoms such as an unexplained runny nose, nausea, and changes in heart rate can be considered mild or early manifestations of nerve agent exposure. Understanding the severity of symptoms is crucial for effective response and treatment in cases of nerve agent poisoning.