Which of the following is a possible physical symptom of a chemical weapons incident?

In the context of a chemical weapons incident, physical symptoms can manifest in various ways depending on the type of agent used and levels of exposure. Headaches are a common reaction to many chemical agents, as they can affect the central nervous system or cause other physiological reactions in the body.

While cold symptoms and unexplained bruises may occasionally be observed in individuals exposed to certain toxins or as a result of other stressors, headaches are particularly indicative and widely recognized in various types of chemical exposure situations, especially those involving organophosphates or nerve agents. Symptoms may emerge suddenly and can often be linked directly to the inhalation or contact with harmful substances.

Thus, selecting only headaches aligns with the characteristic responses typically documented in chemical exposure cases, emphasizing the need for awareness and quick recognition of such symptoms in the context of a chemical weapons incident, while the other options do not directly correlate as strongly or specifically with a chemical weapons scenario.