What is a common sign indicating a flea infestation in a pet?

The presence of constant scratching and hair loss is a strong indicator of a flea infestation in a pet. When fleas bite, they cause irritation and allergic reactions, leading pets to scratch persistently to alleviate the discomfort. Over time, this excessive scratching can result in hair loss, skin infections, and further complications if not addressed.

Fleas not only cause immediate distress but can also lead to other health issues for pets, including anemia or tapeworms. Therefore, observing a pet frequently scratching or showing signs of skin irritation is a critical warning sign that should prompt a closer examination for fleas or consultation with a veterinarian. This behavioral response is much more directly related to flea infestations than the other options, which do not indicate the presence of fleas as clearly.