These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Achievement Unlocked
Critical Research Failure: In the first game, the description for the "Too Much Contra" achievement, obtained from entering the Konami Code, calls it "the level select code from Contra". Putting the Konami Code into Contra gives you thirty lives - it doesn't let you select a level.
Ear Worm - Before you complete or give up, the mellow but persistent trumpeting will infect your skull.
It only gets better with the piano music in the second game.