Boo Who?

Now ---- there just is a cow
Where --- once was a calf
Now ---- there just is a stare
Where --- once was a laugh
Now ---- there just is a bone
Where --- once was a bath
Now ---- a tink-er-y toy
Is ---- an epi-taph
A smile - would make believe
That ---- it had a friend
And ---- tomorrow's name
Once ---- never would end