肉眼

ròu yǎn kàn bu jiàn xì jūn

肉眼看不见细菌。

Bacteria are invisible to the naked eye.

ròu yǎn kě jiàn

肉眼可见

be invisible to the naked eye

ròu yǎn guān chá

肉眼观察

observe with the naked eye

fán fū ròu yǎn

凡夫肉眼

mortal of the mundane world