Expressions (phrases, clauses, etc.), Godan verb with 'mu' ending
one becomes sleepy when one's stomach is full; full stomach, sleepy head; when the skin of the belly is extended, the skin of the eyes droops
Proverb
Also written 腹の皮が突っ張れば目の皮が弛む【はらのかわがつっぱればめのかわがたるむ】