How do you know when a person becomes ill?

A person may show signs of illness through various symptoms, such as persistent coughing, fever, fatigue, or changes in appetite. Behavioral changes, like increased irritability or withdrawal from social activities, can also indicate that something is wrong. Additionally, physical signs such as rash, discoloration, or swelling may be present. It's essential to consider a combination of these factors rather than relying on a single symptom.