手足 ("hand and foot") metaphorises siblings as parts of one body. The idiom is grounded in Tang poet Li Hua's 《
吊古战场文》 ("Lament for the Ancient Battlefield"): 「
谁无兄弟，
如足如手」 — "who has no brothers, like foot, like hand?" — and reinforced by Song writer Su Zhe's memorial 《
为兄轼下狱上书》 pleading for his imprisoned brother Su Shi (recorded in
新华成语词典).
