YOU SAID:

I have a small dog, in his mind, he thinks he is a large dog,

INTO JAPANESE

私は小型犬を飼っていますが、彼の頭の中では、彼は大型犬だと思っています。

BACK INTO ENGLISH

I have a small dog, but in his head I think he is a large dog.

INTO JAPANESE

私は小型犬を飼っていますが、頭の中では大型犬だと思います。

BACK INTO ENGLISH

I have a small dog, but in my head I think it is a large dog.

INTO JAPANESE

私は小型犬を飼っていますが、頭の中では大型犬だと思います。

BACK INTO ENGLISH

I have a small dog, but in my head I think it is a large dog.