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 malfunctioning squib from a poorly constructed dummy round (without propellant, but containing a live bullet and primer) became lodged in the barrel and was fired from the same weapon that had been incorrectly loaded with a blank cartridge, fatally injuring Lee.