A 12-month-old boy presents with intermittent crying for one day. No other symptoms are present—in particular, he did not have fever, vomiting, diarrhea, or urinary frequency. He was in good health before this, with normal growth and development. All immunizations are up to date. He was born via an uncomplicated vaginal delivery, following an unremarkable antenatal period. His family history is unremarkable. There is no history of allergies.