lit. doesn't (even) enter a single aperture (of one's head); I don't understand a word (idiom); it's all Greek to me

a trick; an ingenious method; know-how; the knack (of doing sth)

to get it straight; to start to understand things properly; enlightenment dawns

hole; opening; orifice (of the human body); (fig.) key (to the solution of a problem)

the seven apertures of the human head: 2 eyes, 2 ears, 2 nostrils, 1 mouth