Which of the following behaviors indicates a dog is feeling threatened?

A dog tucking its tail between its legs is a clear behavioral signal that it feels threatened or scared. This posture is a form of submission, indicating that the dog is attempting to make itself appear smaller and less of a threat. In a situation where a dog is feeling anxious, vulnerable, or cornered, tail tucking can be an instinctive response to avoid confrontation or aggression from perceived threats.

The behaviors indicated by the other choices do not suggest a feeling of threat. For example, playful barking typically expresses excitement or a desire to engage in play, while rolling over can be a sign of trust or an invitation for belly rubs, suggesting the dog feels safe. Cocking its head to the side is often a sign of curiosity or trying to understand something better, not fear. Therefore, the behavior of tucking the tail is the most reliable indicator of a dog feeling threatened.