ぐさ
ikigusare

Noun

1. (fish) appearing fresh but actually gone bad

はや かえった ほうがいい、暑 あついから。サバは、生 くされとも われるくらい あし はやい。
hayakukaetta hōga ii atsuikara. sabawa iki kusaretomo iwarerukurai ashiga hayai.
It's hot, so you'd better head back quickly. Mackerel goes off so fast that they coined 'fresh-looking rotten fish'.