Ummm... the actors weren't just improvising the dialogue. The stuff they were saying came from a script. Written by writers. After the voices were recorded, the sound mix was edited, and then it was turned over to animation, who generally work from a precise dialogue breakdown of each individual sound to make the lip synch. Then sound and picture are combined in the final edit. All of which was scrutinized by the directors at every stage. So, it's a pretty safe bet they were almost always saying words that, you know, actually exist.
These cartoons are chock full of WAY too many real errors to go inventing new words.
How about the missing telephone sound effect (can't recall the specific episode)?
Or the missing explosion sound effect in Citizen Ghost?
Numerous instances of characters being colored wrong, so Ray becomes Winston or vice versa.
And the ever-popular misspelled words in the painted backgrounds because the animators were not native English speakers.
But this thread doesn't only have to be about errors.
How cool is it that Ray's Aunt Lois gets mentioned by name in Mr. Sandman long before she appears in the delightfully punny-titled 'Spirit of Aunt Lois'.
Alex