**Core Concept**
Kanavel's sign is a clinical diagnostic criterion used to identify acute suppurative tenosynovitis, particularly in the flexor tendons of the fingers. It is characterized by four cardinal signs: pain on palpation, tenderness, swelling, and a characteristic sausage-like swelling of the affected finger.

**Why the Correct Answer is Right**
The correct answer is associated with the characteristic sausage-like swelling, which is a result of the inflammation and swelling of the flexor tendon sheath. This swelling is due to the accumulation of pus and inflammatory exudate within the tendon sheath. The flexor tendon sheath, composed of fibrous tissue and synovial membrane, becomes inflamed and swollen, leading to the characteristic sausage-like appearance.

**Why Each Wrong Option is Incorrect**
**Option A:** Pain on palpation is one of Kanavel's signs, but it is not the specific characteristic that Kanavel's sign is named for.
**Option B:** Tenderness is another cardinal sign of Kanavel's sign, but it is also not the characteristic that Kanavel's sign is named for.
**Option C:** Swelling is a common feature of many inflammatory conditions, but it is not the specific characteristic that Kanavel's sign is named for.

**Clinical Pearl / High-Yield Fact**
Kanavel's sign is a classic example of a clinical diagnostic criterion that relies on the careful observation of characteristic physical examination findings. Remember that a combination of pain on palpation, tenderness, swelling, and sausage-like swelling of the affected finger is highly suggestive of acute suppurative tenosynovitis.

**Correct Answer: C. Swelling**