**Core Concept**
The "saw-tooth" appearance on a barium enema is a radiological finding that suggests a specific pathology affecting the colon. This phenomenon is due to the presence of a particular type of lesion that causes the colon's normal smooth contour to become irregular.

**Why the Correct Answer is Right**
The saw-tooth appearance is characteristic of **diverticulosis**, a condition where small, bulging pouches (diverticula) form in the wall of the colon. As barium fills these diverticula, it creates a saw-tooth pattern on the X-ray, due to the presence of multiple small, rounded outpouchings. Diverticula are most commonly found in the sigmoid colon, which is why the saw-tooth appearance is often seen in this region.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the saw-tooth appearance on a barium enema. **Option B:** While polyps can cause irregularities in the colon, they typically do not produce a saw-tooth pattern. **Option D:** This option is a red herring, as the saw-tooth appearance is not typically associated with this condition.

**Clinical Pearl / High-Yield Fact**
The saw-tooth appearance on a barium enema is a classic radiological sign of diverticulosis, and is often used to diagnose this condition in patients with symptoms such as abdominal pain, constipation, or changes in bowel habits.

**Correct Answer: C. Diverticulosis.**