At the poker game, the cards move randomly about the table probably due to various different takes needed.
At around 55 minutes the invisible man sprays soda water on Lou and the water in the tank goes down,in the following shot the tank has been refilled.
At around 59 minutes the newsman shows a picture of Louie knocking the guy at the bar out.There was a shot glass on the bar and in the picture the glass is gone,hence the reason they were fighting in the first place.
At around 55 minutes the shot glasses on the bar change places and some disappear in between scenes.
When Lou is shaking Tommy's hand it completely disappear's as if it wasn't there.
The boxer, Tommy Nelson, is invisible and in order to stay this way he must not wear ANY clothes. This would include shoes. And yet when he walks across the mat in the boxing gym his footprints are very apparent, but as if he he wearing shoes and not bare feet.
When Lou goes to see Dr. Turner the psychiatrist, Turner's nameplate misspells his specialty as phychiatry, leaving out the "s".
When the invisible man is eating the spaghetti from Lou's plate the spaghetti is coming from under the table not from Lou's plate.
During the restaurant scene, the meal being consumed by Tommy Nelson would have been seen until fully digested.
When Bud puts down the drink of the second bar guy, you can see the thin wires if you look very carefully.
Since Lou never completes counting out the bribe money that he has found in the box of flowers, Bud could not know that it totals $15,000.
When Lou is on his knees in the ring, the referee counts to six before he tries to rise. Lou however, slightly slips initially and stays briefly on one knee. Technically, therefore, the referee should have continued the count until seven at least.
At the end of the fight when Tommy knocks Rocky out, Boots yells, "Get up, Tommy!" from the audience (instead of "Get up, Rocky!").