**Core Concept**
Decerebrate rigidity is a type of abnormal posture and muscle tone that occurs in patients with damage to the brainstem, particularly the midbrain. This condition is characterized by the extension of the arms and legs, with the arms typically held in a position of extension and the legs in a position of extension and internal rotation.

**Why the Correct Answer is Right**
Decerebrate rigidity is associated with a loss of inhibition of the extensor muscles, leading to an increase in muscle tone and stiffness. This is due to the disruption of the descending reticular formation, which normally exerts an inhibitory influence on the extensor muscles. The affected individual will typically exhibit a positive "decerebrate posture" when placed in a supine position.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because decerebrate rigidity is indeed characterized by the extension of the arms and legs.
**Option B:** This option is incorrect because decerebrate rigidity is associated with a loss of inhibition of the extensor muscles, leading to increased muscle tone and stiffness.
**Option C:** This option is incorrect because decerebrate rigidity is indeed associated with a positive "decerebrate posture" when the affected individual is placed in a supine position.

**Clinical Pearl / High-Yield Fact**
A key feature of decerebrate rigidity is the presence of a positive "decerebrate posture", which is characterized by the extension of the arms and legs, with the arms typically held in a position of extension and the legs in a position of extension and internal rotation. This is a critical differentiator from other forms of abnormal posture and muscle tone.

**Correct Answer:** A. None of the above options is characteristically incorrect about decerebrate rigidity.