Which signals might indicate that a dog feels threatened?

The presence of raised hackles and a stiff posture are strong indicators that a dog feels threatened. Raised hackles occur when the fur along a dog's back stands upright, which is a natural response to stress or fear. This physical change can signify that the dog is trying to appear larger and more intimidating to what it perceives as a threat. A stiff posture, often characterized by a dog standing tall, with tightened muscles and a rigid stance, further supports this interpretation, indicating that the dog is on high alert and may be preparing to react defensively.

In contrast, the other options present behaviors typically associated with relaxation or playfulness. For instance, a wagging tail and playful barking generally suggest that a dog is feeling happy and engaged rather than threatened. Similarly, rolling over and play bowing are classic signals of submission and an invitation to play, exhibiting comfort rather than apprehension. Lastly, sitting quietly with a relaxed expression indicates that the dog is at ease and not feeling threatened. Thus, these behaviors do not align with the signs of threat that are highlighted in the correct choice.