Gomez says "Uranus transits Jupiter," however, such a transit would be impossible to see from Earth.
When Thing hangs up the telephone for Professor Altshuler, and when he hands Morticia the mail, he is a left hand instead of his usual right.
Near the end, when everyone leaves the play room, they leave Gilbert and Hinckley behind. Gilbert's reaction shot is much grainier than that of Hinckley, because it is a zoomed-in version of a wide shot used earlier.