Which of the following is a sign of flea infestation in pets?

Excessive grooming or biting at the skin is a significant sign of flea infestation in pets. When a pet is infested with fleas, the bites can cause irritation and discomfort. As a result, pets often respond by grooming themselves more than usual in an attempt to relieve the itching sensation. This excessive grooming can lead to bald patches, skin infections, or even open sores if the pet continues to bite or scratch at the affected areas.

Increased shed fur can occur for various reasons, including seasonal changes or other skin conditions, but it is not a definitive indicator of fleas. Overexcited behavior can be associated with a wide range of factors, including playfulness or anxiety, and is not a specific symptom of a flea problem. Frequent sleepiness is similarly non-specific and can be attributed to numerous health issues or changes in a pet's environment. Therefore, excessive grooming or biting is a hallmark sign that suggests a flea infestation and warrants further investigation and treatment.