Ok, now all of us Hitchhiker's fans know that in order to translate every known alien language in the universe, you must have a Babel fish in your ear.
Now, in "So Long And Thanks For All The Fish" Arthur Dent returns to Earth and, figuring he'll no longer need it, squeezes the fish out of his ear and keeps it in his fishbowl.
BUT, at the end of "SLATFATF", Arthur goes back into outer space with Ford Prefect, and stays there throughout the next and final book in the series, "Mostly Harmless".
BUT THE BABEL FISH IS NO LONGER IN ARTHUR'S EAR!!!
With that in mind, how is Arthur able to communicate with the other aliens he encounters thereafter?
"So Long And Thanks For All The Fish" and any other book in the Hitchhiker's series