Caltrops in the Shinobi Hiden
The Giyoshu manual is a collection of military articles that were written in 1690. It includes sections on the samurai warfare as well as shinobi no jutsu. In terms of shinobi no jutsu, it includes recipes for blinding powder, the use of caltrops and infiltration and climbing techniques.
It advises shinobi to avoid sleeping naked and mentions how some shinobi trained monkeys to aid them during infiltration. The manual also advocates sipping the water of a river a shinobi needs to cross during cold weather as the enemy would watch the water of a moat to see if it has any movement.
The manual includes a recipe for invisible writing made out of mashed soybeans and water. The mixture would be used as an ink with a new brush and kettle soot would be used to reveal the writing. Old sake rice wine could also be used as an invisible ink. To reveal the writing, it would be held over a fire. Alternatively, the liquid used for tooth dye without the sumac nutgall could be used as invisible ink while water will reveal the writing.