Final answer:
The correct answer is option b. Piloerection is the behavior a dog is least likely to display when attempting to smooth over agonistic tension, as it is usually associated with aggression or anxiety rather than pacification.
Step-by-step explanation:
In the context of animal behavior, particularly for dogs, a display of agonistic tension is an exhibition of behaviors that indicate social conflict which could lead to aggression. When a dog is attempting to reduce or smooth over this tension, various pacifying behaviors may be exhibited. These behaviors are meant to show submission or non-threatening intentions to de-escalate a potentially aggressive situation.
Behaviors such as sniffing, yawning, and tongue flicking are calming signals that dogs use in an attempt to demonstrate peace and avoid conflict. On the other hand, piloerection, which is the bristling of a dog's fur, particularly along the spine, is often associated with arousal and can be a sign of aggression or anxiety rather than an attempt to pacify. Thus, piloerection is the behavior that a dog is least likely to display when trying to reduce agonistic tension and would not be a calming or pacifying signal in this context.