**Core Concept**
Exudative fluid is a type of fluid that accumulates in body cavities due to increased vascular permeability, leading to the leakage of plasma proteins and other substances into the interstitial space. This process is often seen in conditions such as inflammation, infection, or malignancy.

**Why the Correct Answer is Right**
Exudative fluid is characterized by the presence of cellular debris, which is a result of the breakdown of cells and tissues due to inflammation or other pathological processes. This debris can include dead cells, cellular fragments, and other foreign substances that have leaked into the interstitial space. The presence of cellular debris is a key distinguishing feature of exudative fluid, which can be differentiated from transudative fluid, which does not contain cellular debris. The increased vascular permeability allows for the passage of large molecules, including proteins and cellular debris, into the interstitial space.

**Why Each Wrong Option is Incorrect**
**Option A:** Low protein content is actually a characteristic of transudative fluid, not exudative fluid. Exudative fluid typically has a high protein content due to the leakage of plasma proteins into the interstitial space.
**Option B:** Specific gravity < 1.012 is a characteristic of transudative fluid, not exudative fluid. Exudative fluid typically has a higher specific gravity than transudative fluid due to its higher protein content.
**Option C:** Normal vascular permeability is actually the opposite of what occurs in exudative fluid. Exudative fluid is characterized by increased vascular permeability, which allows for the leakage of substances into the interstitial space.

**Clinical Pearl / High-Yield Fact**
When differentiating between exudative and transudative fluid, remember the "3 Ps": protein, pleural, and pulmonary. Exudative fluid is characterized by high protein content, pleural effusion, and pulmonary disease. This mnemonic can help you quickly identify the key features of exudative fluid.

**✓ Correct Answer: D. Cellular debris**