Which of the following is NOT a symptom of a choking agent?

Coughing, tightness of the chest, and nausea are all well-documented symptoms associated with choking agents, which are chemical warfare agents that primarily affect the respiratory system and can cause severe respiratory distress or death.

Coughing occurs as the body attempts to clear the airway from the irritants that choking agents introduce, such as phosgene or chlorine gas. Tightness of the chest can manifest as the airway and lung tissues react to the presence of these harmful chemicals, leading to bronchoconstriction and difficulty in breathing. Nausea may also occur, given that choking agents can induce systemic effects in addition to their local effects on the respiratory system.

On the other hand, blurred vision is not a typical symptom of choking agents. While visual disturbances can occur with different classes of chemical agents, especially those affecting the nervous system or those causing incapacitating effects (like nerve agents), choking agents primarily focus on respiratory effects. Therefore, the absence of blurred vision as a symptom makes it the correct answer in this context.