**Core Concept**
Meckel's diverticulum is a congenital anomaly of the small intestine, resulting from the incomplete obliteration of the vitelline duct. It is a remnant of the omphalomesenteric duct, which connects the yolk sac to the midgut during embryonic development. Meckel's diverticulum can cause complications due to its association with ectopic gastric or pancreatic tissue, leading to acid secretion and potential ulceration.

**Why the Correct Answer is Right**
The most common complication of Meckel's diverticulum is intestinal obstruction, but an uncommon complication is **intestinal hemorrhage due to ectopic gastric mucosa**. This occurs when acid-producing gastric mucosa within the Meckel's diverticulum erodes into adjacent blood vessels, leading to bleeding. The presence of ectopic gastric mucosa is a hallmark of Meckel's diverticulum and is responsible for the majority of complications.

**Why Each Wrong Option is Incorrect**
* **Option A:** Intestinal obstruction is the most common complication of Meckel's diverticulum, not uncommon.
* **Option B:** Infection or abscess formation can occur within Meckel's diverticulum, but it is not the most uncommon complication.
* **Option D:** Intussusception can occur in Meckel's diverticulum, but it is not as uncommon as intestinal hemorrhage.

**Clinical Pearl / High-Yield Fact**
Remember that Meckel's diverticulum is a common congenital anomaly, and its presence should be considered in the differential diagnosis of lower gastrointestinal bleeding in young children or adults.

**Correct Answer:** C.