Drawing of a Huo Guan, from 'Wu Bei Yao Lue (《武備要略》)'.
Huo Guan (火罐, lit. 'Fire pot') is a ceramic grenade used in naval warfare. It is a large ceramic pot filled with explosive gunpowder, poison smoke powder, firecrackers, Di Shu (地鼠, lit. 'Ground rat', a type of firework now known as ground spinner), fragmentation and caltrops. When thrown, Huo Guan will break and explode upon impact, spreading fragmentation and caltrops over a large area. The erratically moving Di Shu distract and confuse the enemy, forcing them to step on the caltrops.