I think he might have a screw loose; he talks to himself all the time.

그는 정신이 좀 이상한 것 같아; 항상 혼잣말을 해.

Only someone who has a screw loose would try to climb that mountain in winter.

정신이 좀 이상한 사람만이 겨울에 저 산을 오르려고 할 거야.