A 9-month-old girl is brought to the emergency department for evaluation after 3 days of poor feeding and 1 day of decreased activity. She is normally breastfed and has recently taken pureed solids. Over 3 days she has shown less interest in feeding and has produced no stools and fewer wet diapers. The day prior to presentation, she was no longer crawling or pulling herself to stand. On the morning of evaluation, she is no longer able to lift her head. WHAT'S THE DIAGNOSIS? READ ON TO FIND MORE CLUES.