**Core Concept**
Paradoxical sleep, also known as REM (Rapid Eye Movement) sleep, is a stage of sleep characterized by low muscle tone, rapid eye movements, and high brain activity, similar to that of being awake. This stage is crucial for memory consolidation, learning, and emotional regulation.

**Why the Correct Answer is Right**
During paradoxical sleep, the body is in a state of relaxation, with decreased muscle tone and reduced metabolic rate. This stage is also associated with increased brain activity, particularly in areas responsible for emotion, learning, and memory. The characteristic brain wave pattern of paradoxical sleep is marked by low voltage, mixed-frequency activity, and high amplitude. This stage is essential for the processing and consolidation of memories, especially emotional ones.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because paradoxical sleep is indeed characterized by rapid eye movements, which are a hallmark of this stage.
**Option B:** This option is incorrect because paradoxical sleep is associated with increased brain activity, not decreased.
**Option C:** This option is incorrect because paradoxical sleep is indeed characterized by low muscle tone, which allows for the characteristic rapid eye movements and other physiological changes associated with this stage.

**Clinical Pearl / High-Yield Fact**
Paradoxical sleep is also known as REM sleep, and it is essential for memory consolidation and learning. Disruptions to paradoxical sleep have been linked to various neurological and psychiatric disorders, including depression and anxiety disorders.

**Correct Answer: C. Low muscle tone.**