Revealing mistake: While fighting Clouseau, Cato sticks a wooden pole through the screen of a television. The screen is made of paper. (00:17:30)
Revealing mistake: When Clouseau answers the phone he shuffles his right foot slightly so that it isn't directly over the spot that Dreyfus drills through a few seconds later. (00:19:45)
Revealing mistake: When Clouseau is on the parallel bars, note the switch as he jumps and turns from Peter Sellers to stuntman, then note again as the stuntman falls down the stairs; the stuntman finishes falling behind the right hand side of the settee, and up pops Peter Sellers on the left hand side of the settee giving the apparant impression he has just fallen down the stairs himself.
Revealing mistake: When Clouseau yanks a man's tooth out, you can still see it; it's just blackened to appear missing.
Revealing mistake: When Clouseau pulls out Dreyfus' tooth there is no blood. (01:31:00)
Revealing mistake: Throughout the whole scene when Clouseau is disguised as a hunchback and is floating out the window, you can see wires.
Revealing mistake: When Clouseau is floating out of his apartment in his costume, in several shots you can see the shadows of the chimney behind him in the sky, indicating this was shot in a studio.
Revealing mistake: When Clouseau strikes Cato on the back of his head with the shinai it's actually just hitting the doorframe to his right with Cato flipping forward on cue.
Revealing mistake: When the castle starts to disappear at the end, lines are visible on the matte painting where the pieces were. As the remainder of the castle disappears, a significant line in the painting is visible on the left side during the remainder of the shot.
Answer: Just Invisible. Besides the fact that his eyeball and eyelid remain intact and in the same position, he returns in a full, visible form (possibly in a film logic borrowed from Looney Tunes cartoons) in the next Panther film.