At the closing scene, the garbage cruncher is chewing away, and Columbo is yelling to Clayton. Clayton reaches up to his ear and yanks down, as if ripping out his hearing aid. Moments later, he does the same thing.
When Clayton is preparing to sneak up to Dudek's room, he meets Columbo at the elevator. He is wearing his hearing aid. As he comes out of the elevator, the hearing aid is out. He hides close to Dudek's room and then walks in... wearing the hearing aid again.
(After discovering that the toothbrush in Dudek's suitcase is not his but his roommate's)
Mazoor Berozski: Lieutenant, then Tomlin Dudek could not have packed his own suitcase.
Columbo: That's what I was trying to get around to, sir, yes. And if somebody else packed it who didn't know that he wore dentures then...
Berozski: Then his accident was not an accident!
Columbo: I, uh, thought you'd like to know, sir, that, uh, I think that is a possibility, yes sir.
Columbo: The murderer just had to be a deaf man.
90 minutes long.