Which of the following is a sign of internal abdominal bleeding?

A rigid abdomen is a significant indicator of internal abdominal bleeding. This condition occurs when there is irritation of the peritoneum, which is the lining of the abdominal cavity. When blood accumulates in the abdominal cavity, it can lead to inflammation and muscle tension, causing the abdominal muscles to become stiff and rigid.

Typically, this rigidity suggests a serious underlying issue, such as a lacerated organ or significant hemorrhage within the abdomen, prompting immediate medical evaluation and intervention. This symptom stands out as it indicates an acute condition that needs to be addressed quickly to prevent more severe complications.

The other options represent symptoms that may be associated with various medical conditions but do not specifically indicate internal abdominal bleeding. Poor appetite and increased thirst can occur in different situations, and while a rapid heart rate can signal distress, it is not exclusive to internal bleeding as it can arise due to various other reasons, including pain, anxiety, or dehydration. Hence, a rigid abdomen is a more definitive sign of internal bleeding in this context.