When you die several times in short order, you'll gain the option to equip a special piece of gear called the Chicken Hat. While this is equipped, enemies won't engage with you no matter how obvious you make your presence. Instead, they'll pass out while standing. However, it only works three times in a given mission before disappearing on the fourth use, and you won't be able to rank higher than "A" on that particular run. You can enable or disable the special gear from the Options menu, while the game is paused.