Makibishi

Makibishi are small, sharp objects that are mainly used to inhibit someone from walking in a certain direction or area, since they would injure the ninja's feet if they tried to walk over them.

Trivia

 * Although being rarely used in Naruto, they're commonly a selectable tool in video games such as Naruto: Ultimate Ninja Heroes.
 * In the prologue novelisation, Kakashi's makibishi are drenched in poison.