"Your duck is my dinner."
To expand on what flaze said, "your" is a possessive adjective, so it is always used with a noun: your house, your cat, etc. "Yours" is a possessive pronoun, which replaces the noun: This is my book, that is yours. In this case "yours" replaces "your book".
- This is MY pen. So it's MINE.
- This is YOUR car. So it's YOURS.
- This is HIS phone. So it's HIS.
- This is HER hat. So it's HERS.
- This is OUR country. So it's OURS.
- This is THEIR house. So it's THEIRS.