Which of the following abdominal signs is seen in this patient with intestinal infection? A 35-year-old male presents to the emergency department with 8-9 episodes of watery diarrhea and 4-5 episodes of vomiting since returning from a trip to Ningbo yesterday. On examination: dry lips and skin, BP 90/56 mmHg, soft abdomen, no hepatosplenomegaly, active bowel sounds. Stool microscopy shows rapidly motile bacteria with darting movements.