YOU SAID:

the dog eats the cat's food quickly with a grin

INTO JAPANESE

その犬はにやにや笑って猫の食べ物を素早く食べます

BACK INTO ENGLISH

The dog grins and quickly eats the cat's food

INTO JAPANESE

犬はニヤリと笑い、猫の餌を素早く食べます

BACK INTO ENGLISH

The dog grins and quickly eats the cat's food