At the end of the movie, the football filled with flubber gas is seen floating among a series of man-made satellites. They are the same satellites used in Eyes in Outer Space (1959).
Professor Ned Brainard: The road to genius is paved with fumble-footing and bumbling. Anyone who falls flat on his face is at least moving in the right direction: forward. And the fellow who makes the most mistakes may be the one who will save the neck of the whole world some day.
Mr. Harker: Your tax bill for the first three Quarters of the current year. The figure includes delinquent penalties of $12,895 at 5% for the first two Quarters. All based on an estimate of projected earnings, of course.