Vladimir Nabokov’s 1962 novel Pale Fire includes a character named John Shade, a poet who writes the lines

Space is a swarming in the eyes; and time,
A singing in the ears.

In the first edition of his 1964 book The Ambidextrous Universe, Martin Gardner quoted these lines and, as a joke, credited them to Shade rather than Nabokov, listing Shade in the index.

Nabokov, in turn, in his 1969 novel Ada or Ardor: A Family Chronicle had a character quote Gardner’s book and the same two lines of verse:

‘Space is a swarming in the eyes, and Time a singing in the ears,” says John Shade, a modern poet, as quoted by an invented philosopher (‘Martin Gardiner’) in The Ambidextrous Universe, page 165.

Gardner’s book concerns symmetry, and Ada is a palindrome; further, the action in that novel takes place on Anti-Terra, a sort of mirror image of Earth. Nabokov’s 1974 novel Look at the Harlequins!, also influenced by Gardner’s book, concerns a man who can’t distinguish left from right.

(Thanks, Jeff.)