It could be the next line to a well known poem, passage from a book, a song lyric, a familiar saying…anything recognisable and well known.
Provide the first line or two, or at least enough to provide a clue to what follows.
Hell…if it's funny or fits in with the post, it doesn't even have to be the “official” next bit…this is all just for fun.
As an example : “O Romeo, Romeo!” ; the answer would be : “wherefore art thou Romeo?” from Shakespeare's 'Romeo and Juliet'.
It's not necessary to provide the source, just the missing part.
Here's one to start things off : post the next part and then leave something for the next person to complete.
Mama, just killed a man
Put a gun against his head….