腐る
くさる · kusaru · JLPT N3 · verb-godan
to rot
🍎🦠 kusaru is kin to kusai (smelly): whatever rots starts to stink
The kanji 腐 is 府 (storehouse) over 肉 (meat): meat left sitting in storage goes bad. For the sound, think of kusai, the word for smelly; kusaru is what food does just before it becomes kusai.