Throw It In: There's a moment where Maitland has Axel and Jenny cornered and is deciding what to do with them when he stop in his tracks and makes a face. In reality, the actor was reacting to something Eddie Murphy ad-libbed but was removed in editing. They kept in his reaction because it made Maitland seem even more sinister and unhinged.
There are a spectacular number of ad-libs in this movie in general, most of them from Murphy.
Unintentional Period Piece: The first film is very much a product of 1984 from the clothing to the music to the pop culture references.
Amusingly, Stallone had a bunch of ideas about how the movie should go and was editing the script accordingly. When Murphy was brought on, Stallone gracefully backed out, taking the ideas with him to be used in Cobra.