Years ago, when I was flying a Rollason Condor near Biggin Hill, I heard a panicked voice on the frequency: "I see a pink pig. A PINK PIG!!" He thought he was hallucinating. A very calm controller talked him into flying away from it and concentrating on getting back to the field and landing. The poor chap sounded quite shaken.
Later we heard that a balloon in the shape of a pig, tethered at the Virgin building, had escaped its moorings.