What tactical conditions might indicate the use of biological weapons?

The use of biological weapons might be indicated by an increase in dead or sick animals and insects due to the nature of biological agents. These agents are often designed to target living organisms, and observing unusual mortality rates or illness in animal populations can be a significant indicator of their employment. In many cases, biological pathogens can adversely affect wildlife before humans show visible symptoms, making alterations in animal health a critical warning sign.

This phenomena occurs because biological weapons are designed to spread through biological means - such as insects (vectors) or through environmental contact. Therefore, if a region experiences a noticeable rise in the population of sick or deceased animals and insects, it may suggest a biological attack is in progress or has occurred, emphasizing the need for surveillance and assessment by military and public health organizations.

In contrast, the other options, while indicative of different tactical scenarios, do not directly correlate with the use of biological weapons, focusing instead on conventional warfare elements or reconnaissance activity. Observing dead or sick animals serves as a more specific warning related to biological threats.