Be A Ninja is a ninja manual that is only seen in "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 a red case-bound book, the front of which has an image of a classic ninja with red, Japanese-like text. On the back are two crossed katana with a shuriken in the middle.
- The "Smokebomb boogers" gesture that Jake performed is not possible to do unless a person has Stretchy Powers like Jake.