Final answer:
Infants exhibit signs of pain through behaviors like irritability and limpness, along with physical symptoms such as apnea, seizures, and changed feeding habits.
Step-by-step explanation:
Infants may show signs of pain through various behaviors and physical symptoms other than crying. These signs include irritability, difficulty waking, limpness, and changes in regular activities such as feeding and sleeping. More serious symptoms indicating pain or illness could include hypotension (low blood pressure), apnea (cessation of breathing), bradycardia (slow heart rate), temperature instability, seizures, bulging fontanel, stiff neck, hemiparesis, and opisthotonos. It's imperative to observe these signs carefully because infants cannot verbally express their discomfort.