Which of the following is a common sign of fear or stress observed in cats?

Dilated pupils are a widely recognized sign of fear or stress in cats. When a cat experiences fear or anxiety, its body reacts by triggering the sympathetic nervous system, leading to a physiological response known as the "fight or flight" response. This response can cause the pupils to dilate in order to allow more light in, which may help the cat to see better in a potentially threatening situation.

In the context of assessing a cat’s emotional state, observing dilated pupils can provide valuable information about the level of stress or fear the animal may be experiencing. Caregivers and veterinary professionals can use this sign to tailor their behavior and the animal's environment to help reduce anxiety and create a more calming atmosphere.

Quick breathing, a hunched back, and loud meowing can also indicate discomfort or distress but may not consistently signify fear in the same way that dilated pupils do. Therefore, while those signs can be associated with stress, dilated pupils are particularly recognized as a direct indication of the fear response in cats.