**Core Concept**
The most probable diagnosis in this clinical scenario involves a bacterial infection affecting the intestinal tract of a 6-month-old infant, leading to bloody diarrhea, abdominal distension, and severe pain.

**Why the Correct Answer is Right**
The symptoms described are characteristic of intussusception, a condition where a part of the intestine telescopes into another, causing bowel obstruction and ischemia. This condition often leads to bloody stools due to the ischemia and subsequent mucosal damage. The infant's age and the sudden onset of symptoms, combined with the presence of abdominal distension and pain, further support this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Gastroenteritis is a common cause of diarrhea in infants, but it typically presents with non-bloody stools, and the infant's age and symptoms do not align with a typical gastroenteritis presentation.

**Option B:** Hirschsprung's disease is a congenital condition affecting the colon, but it typically presents with chronic constipation and abdominal distension, not acute bloody diarrhea.

**Option C:** Intestinal obstruction due to volvulus or other causes may present with abdominal distension and vomiting, but the presence of bloody diarrhea and the infant's age make intussusception a more likely diagnosis.

**Clinical Pearl / High-Yield Fact**
Intussusception is a medical emergency and requires prompt diagnosis and treatment to prevent bowel ischemia and necrosis. The infant's screaming on examination is a red flag for intussusception, as it indicates severe abdominal pain.

**Correct Answer:** C. Intussusception.