William Goldman originally wrote several drafts of the screenplay, all of which were rejected, as he wrote it as a simple comedy, and the producers preferred to use the film to "explore the loneliness of invisibility". Eventually, he left the project, though he still receives a screenplay credit. He claims never to have seen the movie, and thus cannot say for sure how much of his material is actually in the film.
The picture was not the first invisible man comedy. Disney's 1972 film Now You See Him, Now You Don't (1972) and 1951's Abbott and Costello Meet the Invisible Man (1951) preceded it.
Nick is wearing a three piece suit when he goes to the seminar, but when he wakes up after the accident, he is only wearing a two piece suit. Not the vest. Nick tried to put on the vest when he was hurrying to leave his apartment. It was too difficult so he throws it aside.
An invisible man would be blind, the only way to see is for light to reflect off the back of the retina. If the retina is invisible the light would pass through.
When Nick is eating dinner with Alice, he is wearing make-up, goggles and a wig to disguise his invisibility. However you can also see his tongue when he is talking. Making his tongue visible seems unlikely nor was established.
David Jenkins: Perhaps a small reminder of the state of things is in order. I'm the one who kills people, Warren, not you. And if you screw up with me, I will cut off your testicles, I will lightly fry them, and Morrissey here...