This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Not a feature of REM sleep: 
Select and explain. 
A. Bruxism, B. Irregular breathing, C. Muscle tone in the body is depressed, D. Is associated with active dreaming
A: Bruxism
Answer: A: Bruxism 
Explanation: Bruxism REF: GUYTON & HALL, Ganong, various internet resources. See APPENDIX-11 for "SLEEP PHYSIOLOGY"