**Core Concept**
The left side of the colon, specifically the sigmoid colon and rectum, has distinct features that differentiate it from the right side of the colon. These features are related to its blood supply, lymphatic drainage, and the type of cancer that commonly arises in this region.

**Why the Correct Answer is Right**
Left-sided colon cancer, often involving the sigmoid colon or rectum, typically presents with changes in bowel habit, such as constipation or diarrhea. This is due to the involvement of the parasympathetic nerves that regulate bowel motility. Additionally, left-sided colon cancer often leads to iron deficiency anemia (IDA) due to chronic blood loss from the tumor. This is because the left side of the colon has a rich blood supply, particularly from the superior rectal artery, which is a branch of the inferior mesenteric artery. The anemia is often non-microcytic, as the blood loss is usually occult and not associated with significant iron deficiency.

**Why Each Wrong Option is Incorrect**
**Option A:** Anemia is indeed a feature of left-sided colon cancer, but it is not the most distinctive or common symptom.
**Option B:** Obstruction is more commonly associated with right-sided colon cancer due to the narrower diameter of the cecum and ascending colon.
**Option C:** Altered bowel habit is a feature of left-sided colon cancer, but it is not unique to this location.
**Option D:** Melena is more commonly associated with upper gastrointestinal bleeding, not left-sided colon cancer.
**Option E:** Feculent vomiting is more commonly associated with high-grade bowel obstruction, often seen in right-sided colon cancer.

**Clinical Pearl / High-Yield Fact**
Left-sided colon cancer often presents with changes in bowel habit, and iron deficiency anemia is a common feature due to occult blood loss from the tumor.

**Correct Answer: C. Altered bowel habit**