I watched from the jumpseat of a Gemini MD-11 jumpseat as a captain made the hardest landing I'd ever seen. It was in Campinas Brazil.
We congratulated ourselves on surviving as we slowed to taxi speed. Then the tower said, "Geemeenee, notify your maintenance, you left a piece of the plane on the runway...."
It was one of the "canoes" - the fiberglass flap track covers.....