In dogs, it is used to refer to a dog with an abnormal, sometimes extreme, level of arousal in response to what would be a normal stimulus.
reference: Pat Miller, CBCC-KA, CPDT-KA 2021, Reactive Behavior in Dogs, Whole Dog Journal, accessed 21 April 2024, <https://www.whole-dog-journal.com/training/reactive-dog-behavior/>
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