YOU SAID:

My dog eats cats very fast.

INTO JAPANESE

私の犬は猫を非常に速く食べる。

BACK INTO ENGLISH

My dog ​​eats a cat very quickly.

INTO JAPANESE

私の犬は非常に迅速に猫を食べる。

BACK INTO ENGLISH

My dog is eating cat very quickly.

INTO JAPANESE

私の犬は、非常に迅速に猫を食べています。

BACK INTO ENGLISH

My dog is eating cat very quickly.