Which of the following is a sign of internal bleeding?

The ability to taste iron in the mouth is indicative of internal bleeding because this symptom often relates to the presence of blood in the gastrointestinal tract. When blood is digested, it can result in a metallic taste, which is often described as tasting iron. This taste occurs due to the iron content in the hemoglobin present in the blood, thereby serving as a signal that there may be bleeding occurring internally.

Other symptoms related to internal bleeding might include faintness and weakness, which could suggest a drop in blood volume due to significant bleeding, but they are less specific than the metallic taste linked directly to blood. Similarly, while skin turning yellow may occur in various medical conditions, it is more associated with liver issues or jaundice, rather than internal bleeding. A severe headache could indicate a number of conditions, including potential intracranial issues, but it does not specifically signal internal bleeding in the same way as the ability to taste iron does. Thus, the ability to taste iron in the mouth signifies internal bleeding most directly.