Body Pop is a feature in SFH3. It means that a character loses all his limbs and his body pieces (arms, legs, body and head) can move around the map.
Weapons that do body pop are all Blades, but sometimes it can happen with Explosives and Shotguns.
And when the character is frozen in ice, if they gets killed, they will body pop. Dragon's Breath always does body pop. A game modifier called Tin Man makes each character body pop after death.