Angel uses his backpack as a territorial marker.
Territorial marking is a term to refer to a series of instinctive behaviors of animals and humans to delimit and defend their territory.
Generally, mammals usually mark the limits of their territory using body fluids such as urine and stools so that when another mammal passes through this place they recognize the smell and move away from that territory.
In the case of humans, territoriality is not like in animals. However, instinctively we have certain territorial behaviors like Angel's on the bus because by putting his suitcase on the seat next to him he is marking the place as his to prevent someone from invading him.
Note: This question is incomplete because the options are missing. Here are the options:
A) territorial marker
B) regulator
C) backchannel cue
D) adapter
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