窍

Top cave radical — a roof shape above a stylized cavity, picturing a cave dwelling. The indexing radical, anchors 窍 in the family of opening/hole chars: 穿 pierce, 空 empty, 突 sudden / protrude, 窗 window, 究 investigate. Marks 窍 as an aperture — both literal body orifices (七窍 the seven orifices) and the figurative 'opening / knack' in 诀窍 know-how.

Bottom 巧 supplies the sound — qiǎo shifting to qiào with tone change. Also adds a faint semantic flavor: a clever opening / a knack — fitting the modern figurative sense of 窍 (诀窍 is the key trick to doing something well). Same phonetic family: 朽 rotten, 杇 trowel. Simplified from traditional 竅, which had the much busier 敫 phonetic on the bottom.