A squib from an improperly made dummy round (no powder charge, but with a bullet and a live primer) from a previous scene was stuck inside the barrel and propelled from the same weapon which had been negligently loaded with a blank cartridge, striking Lee in the abdomen and killing him.
A defective cartridge from a faulty dummy round (lacking powder, but containing a live projectile and primer) became lodged in the barrel and was fired from the same gun that had been carelessly loaded with a blank cartridge, striking Lee in the abdomen and ultimately causing his death.