YOU SAID:
He is smiling while walking to the sports center with his hamster.
INTO JAPANESE
彼は彼のハムスターとスポーツ センターを歩きながら笑っています。
BACK INTO ENGLISH
He laughed while walking his hamster and a sports centre.
INTO JAPANESE
彼は彼のハムスターとスポーツ センターを歩きながら笑った。
BACK INTO ENGLISH
He laughed while walking his hamster and a sports centre.
You've done this before, haven't you.