YOU SAID:

You never know when a dog will eat a bird's head

INTO JAPANESE

犬がいつ鳥の頭を食べるかわからない

BACK INTO ENGLISH

I don't know when a dog eats a bird's head

INTO JAPANESE

犬がいつ鳥の頭を食べるのかわからない

BACK INTO ENGLISH

I don't know when a dog eats a bird's head