**Core Concept**
The "Bird of Prey" sign, also known as the "bird beak" sign, is a radiographic finding observed during barium studies of the gastrointestinal tract. It is characterized by the tapering of the bowel lumen, resembling the beak of a bird, which is indicative of a specific type of intestinal obstruction.

**Why the Correct Answer is Right**
In the context of sigmoid volvulus, the "Bird of Prey" sign is a characteristic feature on barium enema studies. This sign is due to the twisting of the sigmoid colon around its mesenteric axis, leading to a tapering of the bowel lumen and a characteristic appearance on the radiograph. The twisted sigmoid colon appears as a narrow, tapering structure, resembling the beak of a bird, which is the hallmark of this sign.

**Why Each Wrong Option is Incorrect**
**Option A:** Gastric volvulus is a condition where the stomach twists around its mesenteric axis, but it does not typically present with the "Bird of Prey" sign on barium studies. Gastric volvulus may present with a variety of radiographic findings, including a "U" or "C" shape appearance of the stomach.

**Option B:** Intussusception is a condition where a segment of the intestine telescopes into another segment, leading to intestinal obstruction. While intussusception can present with a variety of radiographic findings, the "Bird of Prey" sign is not typically associated with this condition.

**Option D:** Caecal volvulus is a rare condition where the caecum twists around its mesenteric axis, leading to intestinal obstruction. While caecal volvulus can present with a variety of radiographic findings, the "Bird of Prey" sign is not typically associated with this condition.

**Clinical Pearl / High-Yield Fact**
The "Bird of Prey" sign is a classic radiographic finding in sigmoid volvulus, and its presence should prompt immediate consideration of this diagnosis. In addition to the radiographic findings, patients with sigmoid volvulus may present with abdominal pain, constipation, and vomiting.

✓ Correct Answer: C. Sigmoid volvulus