What does the term "piggyback" refer to in the context of bullet trajectories?

The term "piggyback" in the context of bullet trajectories refers to two bullets that exit a firearm in tandem, meaning they leave the barrel very closely spaced in time and trajectory. This can occur in certain specific conditions, such as when multiple projectiles are fired simultaneously or when a malfunction in the firearm allows for the discharge of two rounds without a complete separation of the firing process.

Understanding this concept is important in forensic investigations, as it can have implications for the analysis of crime scenes and ballistic trajectories. The examination of bullet wounds, the pattern of trajectory, and the number of bullets involved can provide crucial evidence regarding the shooting incident. The focus on "exiting in tandem" distinguishes this phenomenon from other options that do not accurately depict the spatial and timing characteristics of bullets as they travel together closely.