A nurse is perfоrming а develоpmentаl аssessment оn a 5-month-old infant during a well-child visit. The parent reports that the infant smiles, turns toward voices, and opens the mouth when hungry. During the assessment, the nurse strokes the sole of the infant’s foot and notes that the toes fan outward. The nurse also observes that the infant’s head falls backward when pulled from a supine to a sitting position. Which finding requires follow-up?