I consciously noted details of their faces. (Para. 15)
Meaning: I looked carefully on purpose at their faces and paid attention to the personal specific parts of them.
detail: n. a small part or piece
When I read I can never remember the details. 我看书时，总是记不住细节。
We failed the test because many of the questions were about details. 我们考试没通过，因为许多问题都是关于细节方面的内容。