## Core Concept
Decerebrate rigidity, described by Sir Charles Sherrington, is a condition characterized by increased muscle tone in the extensor muscles of the limbs following a midbrain transection. This phenomenon helps in understanding the role of the brainstem in regulating muscle tone and posture.

## Why the Correct Answer is Right
Decerebrate rigidity involves an increase in extensor tone due to the loss of inhibitory influences from higher centers on the vestibular nuclei and the lateral vestibulospinal tract, which then facilitates extensor reflexes. This results in the characteristic posture of decerebrate animals (or humans), with extended limbs.

## Why Each Wrong Option is Incorrect
- **Option A:** Increased extensor tone is indeed a feature of decerebrate rigidity, making this option incorrect as an "except" choice.
- **Option B:** This option might relate to a feature that could be associated with decerebrate rigidity or not; without specifics, we acknowledge that characteristics like opisthotonus (arching of the back) are seen.
- **Option C:** Typically, decerebrate rigidity involves increased tone in extensor muscles rather than flexor muscles, which are more associated with decorticate rigidity.

## Clinical Pearl / High-Yield Fact
A key clinical correlation is that decerebrate rigidity often results from a lesion at the level of the lower pons or upper medulla, leading to a characteristic posture with the limbs extended. This contrasts with decorticate rigidity, which results from lesions above the level of the brainstem and leads to flexion of the upper limbs and extension of the lower limbs.

## Correct Answer: C.