Kotowaza of the day: Share your innard self

Japanese:

肝胆相照らす

Romanized:

Kan-tan ai terasu

Meaning of Japanese:

To have a mutually intimate understanding*

English equivalents:

(To be) bosom buddies, inseparable friends

*This kotowaza defies easy explanation. Literally it means to have shed light on one another's liver (肝臓) and gall bladder (胆嚢). At first I thought the English meaning derived from the fact that the gall bladder is nestled in all comfy with the liver. But it seems that the liver and gall bladder, as a pair, are symbolic in Japanese and Chinese - from which this saying originated - for "the bottom of one's heart." Hence, when close friends share their most intimate thoughts, they have illuminated one anothers' liver and gall bladder (肝胆).