Be A Ninja is a ninja manual, only seen in episode "The Chamber of Frozen Blades." Jake is seen reading it at the beginning of the episode. Jake says he and Finn found it in a ditch. The book claims that through a series of listed hand gestures, you can turn your boogers into smoke bombs, but nothing more is known about its contents.
It is red case-bound book. The front of the book has an image of a classic ninja with red, Japanese-like text that states "Be A Ninja." On the back are two crossing katanas (samurai swords) with a shuriken (Ninja star) in the middle.
- The "Smokebomb boogers" gesture that Jake showed is not possible for a person to do unless the person has Stretchy Powers like Jake.