YOU SAID:
karl is a poo poo head
INTO JAPANESE
カールはうんちの頭です
BACK INTO ENGLISH
Carl is a poop head
INTO JAPANESE
カールはうんこ頭だよ
BACK INTO ENGLISH
Carl has a poop head
INTO JAPANESE
カールの頭はうんこです
BACK INTO ENGLISH
Carl's head is poop
INTO JAPANESE
カールの頭はうんちです
BACK INTO ENGLISH
Carl's head is poop
That didn't even make that much sense in English.