Okay, let's tackle this question. The scenario is an infant waking up at night with abdominal pain that's relieved by passing red stools. The key here is to think about conditions that cause colicky pain and are relieved by defecation. The red stools suggest blood, so maybe something involving the gastrointestinal tract with bleeding.

First, the core concept here is probably intestinal obstruction or a condition causing intussusception, which is common in infants. Intussusception occurs when one segment of the intestine telescopes into another, leading to obstruction and possible ischemia. The classic presentation includes colicky pain, vomiting, and bloody stools which might look like "currant jelly" due to mucus and blood. But wait, the question mentions red stools, which could be similar but maybe different in color. Alternatively, could it be something like milk protein allergy causing bloody stools? No, that's usually with formula-fed infants and the stools are more like "currant jelly" again. Wait, maybe the red stools are due to bright red blood, which might point to a different cause. Another possibility is Meckel's diverticulum, which can cause pain and bleeding, but that's more common in toddlers. Or maybe a foreign body? But the relief after passing the stool is a key point here. Intussusception is often relieved when the bowel reduces, which can happen with defecation.

The correct answer is likely intussusception. Let me check the options again. The options aren't listed, but the correct answer is probably intussusception. Now, why are the other options incorrect? Let's think. If the options included milk allergy, that's usually with other symptoms like diarrhea or eczema. If there's Hirschsprung's disease, it's more chronic with constipation, but acute cases can present with obstruction. Necrotizing enterocolitis is more common in preterm infants and presents with other signs like abdominal distension and sepsis. So the wrong options would be those without the typical presentation of intussusception. The clinical pearl here is that intussusception in infants often presents with sudden onset pain, vomiting, and stools with blood and mucus, and it's a common cause of intestinal obstruction in this age group. The key is the relief after passing the stool, which fits with the telescoping reducing during a bowel movement.

**Core Concept**
This question tests recognition of **acute intestinal obstruction** in infants, particularly **intussusception**, which is a telescoping of one segment of the intestine into another. The hallmark presentation includes **colicky abdominal pain, vomiting, and currant jelly stools** (mucus and blood). Relief after defecation is a key clue.

**Why the Correct Answer is Right**
**Intussusception** occurs when a segment of the intestine slides into an adjacent segment, causing obstruction and reduced blood flow. The pain is intermittent and colicky due to peristalsis against the blockage. Bright red blood in stools (as described here) is due to mucosal injury and ischemia. Passage of stool relieves pressure, temporarily reducing the obstruction and pain. The classic age group is **6–24 months**, aligning with the infant’s age in the question.

**Why Each Wrong Option is Incorrect**
**Option A:** *Milk protein allergy* causes **chronic bloody stools

✓ Correct Answer: D. Intussusception