YOU SAID:

I have a cat in my pants.

INTO JAPANESE

私のズボンに猫があります。

BACK INTO ENGLISH

Have a cat in my pants.

INTO JAPANESE

猫が私のズボンであります。

BACK INTO ENGLISH

The cat is in my pants.

INTO JAPANESE

猫は私のズボンです。

BACK INTO ENGLISH

The cat is in my pants.