摸不着头脑 (摸不著頭腦) mōbùzháo tóunǎo

mōbùzháo tóunǎo phrase to be unable to make any sense of the matter; to be at a loss
Domain: Modern Chinese 现代汉语
Notes: (CC-CEDICT '摸不著頭腦')

Also contained in

丈二和尚,摸不着头脑