Which of the following is a sign of a medical emergency?

Choking is indeed a sign of a medical emergency because it poses an immediate threat to a person's airway and ability to breathe. When someone is choking, the obstruction in the airway can lead to a lack of oxygen, which can result in serious consequences, including unconsciousness or death if not addressed promptly. Recognizing choking as a critical situation requires immediate action, such as performing the Heimlich maneuver or calling for emergency help.

In contrast, the other choices—feeling tired, minor cuts, and infrequent headaches—are generally not considered medical emergencies. Feeling tired can stem from a range of causes, some of which may be temporary or easily manageable. Minor cuts typically can be treated with basic first aid and don’t usually require urgent medical intervention, while infrequent headaches may be a common occurrence and might not indicate a serious health issue unless accompanied by other alarming symptoms. Therefore, choking is the only situation listed that warrants immediate response due to its potential life-threatening nature.