YOU SAID:

I hit my cat with a car and decided to throw it in a river

INTO JAPANESE

猫を車で殴り、川に投げ込むことにしました

BACK INTO ENGLISH

I decided to hit the cat in the car and throw it into the river

INTO JAPANESE

車の中で猫を殴って川に投げ込むことにした

BACK INTO ENGLISH

I decided to hit the cat in the car and throw it into the river