What is characteristic of the hemoptysis associated with plague?

The characteristic of hemoptysis associated with plague is bright red blood. This is indicative of fresh blood that originates from the lungs, suggesting active bleeding. In the context of plague, particularly the pneumonic form, this kind of hemoptysis can occur due to lung damage caused by the infection, and the bright red appearance of the blood indicates oxygen-rich blood being coughed up, which tends to happen when there is significant damage to the lung tissue or vasculature.

In contrast, dark red blood typically suggests older blood, which would have undergone changes from prolonged interaction with tissues, possibly indicating a different etiology or source of bleeding, such as in chronic lung conditions. Thin, watery blood might suggest a mix with other fluids or a different type of pathology not typical of infectious processes like plague. Foamy blood is often associated with pulmonary edema or the presence of air in the blood, which does not typically align with the expected presentation of hemoptysis in plague. Therefore, bright red blood is the defining feature in this scenario.