Final answer:
Context effects refer to how the surrounding environment or situation can influence our perception of stimuli. In this case, when people are holding a gun themselves, they are more likely to perceive another person as also holding a gun.
Step-by-step explanation:
The phenomenon described in the question is an example of context effects on perception. Context effects refer to how the surrounding environment or situation can influence our perception of stimuli. In this case, when people are holding a gun themselves, they are more likely to perceive another person as also holding a gun, rather than perceiving them as holding a phone or wallet.