The infamous head-bump has to be one of the most well-known flubs in the Star Wars canon. If you look to the right in the above GIF, you can see some poor extra knocking his noggin against the metal door. You can't really blame whoever was in the suit -- it's probably impossible to see out of those helmets; and it probably doesn't help that they were a little tall for a stormtrooper.
However unintentional, keeping this error in the film has added to the mythos of the Empire's hilariously inept ground forces. It's such a beloved in-joke that a special nod was included in Attack of the Clones.
That's Jango Fett boarding his ship, bumping his head on the metal door (you can even hear the metallic "bonk" in the actual scene). It does sort of lose something in the translation; the old flub was a product of genuine error and oversight, whereas this is just a cold CGI recreation. Then again, it makes a bit of sense if you consider the fact that Stormtroopers are clones of Jango Fett, and would inherit that clumsiness. Which also explains why a world-class bounty hunter like Boba Fett could die at the hands of a frightened and bewildered blind man.
If you're not familiar with IG-88 (center), he's part of the badass lineup of bounty hunters assembled on Darth Vader's ship in The Empire Strikes Back. As the only droid bounty hunter -- unless you count 4-LOM, which nobody really does -- IG-88 kind of sticks out. Which is why it's strange that, up to this point, you never noticed that several IG-88 heads were lined up in the Cantina in A New Hope.
It's hard to tell what function those heads originally served in a bar setting, but it kind of looks like they might be some sort of tap for blue milk or space beer or whatever butt-chinned frogmen drink. That, or Wookie-sized Martini shakers. Whatever use they were in the Cantina, it's obvious that one of the trinkets was stripped by the Star Wars crew and repurposed for the creation of IG-88. That, or those heads stand as a warning to droids who insist on being served by the robot-racist bartender.
One of the best hidden bits in the entire franchise occurs in the opening minutes of the very first movie, as the Imperial Star Destroyer chases down the rebel ship Tantive IV. Being the 70s, these ships were naturally hand-crafted models, which left room for the creators to leave their own mark, however depraved it may be. As the legend goes, one of the workshoppers stuck tiny posters into the cockpit of the Tantive IV, one of which is a Playboy centerfold. It's impossible to see in motion on the available transfers, but you can clearly see them in the model taken apart from the movie.
That's the Playboy poster on the right and a... super-small Star Wars movie poster on the left. That second poster has staggering implications for the entire universe of the franchise. I mean, who would have thought Han Solo was a total nerd?