At the length of 9 minutes and 48 seconds, "Horton Hatches the Egg" is the longest Looney Tunes or Merrie Melodies short ever made.
The song Horton is singing , but doesn't know the words to is 'The Hut-Sut Song', a popular novelty song from the early '40s.
Peter Lorre was a favorite characterization for the famed Warner Bros. cartoonists, as he tangled several times with Bugs Bunny and Daffy Duck. He was also portrayed as a fish in a Dr. Seuss/Warner Bros.' short, "Horton Hatches the Egg".
Dr. Seuss claimed that he was inspired to write "Horton Hatches the Egg" due to a minor accident. Wind blew through an open window in his studio, and messed up his sketches. A sketch of an elephant ended atop a sketch of a tree, creating a "fortuitous juxtaposition". Seuss decided to write a story about the image.