A 14-month-old boy presents to the emergency department with a 6-hour history of intermittent colicky abdominal pain, two episodes of bilious vomiting, and the mother reports the child passed a stool that looked like "jam mixed with mucus" 2 hours ago. On examination, a sausage-shaped mass is palpated in the right upper quadrant. The stool appearance marked **A** in the diagram is described as dark red currant jelly stool. Which of the following best explains why this finding represents a LATE sign of intussusception rather than an early sign?