What is a common behavioral issue in horses that may indicate stress or boredom?

Cribbing is a common behavioral issue in horses that is often indicative of stress, anxiety, or boredom. This behavior involves the horse grasping a solid object, such as a fence or a stall door, with its teeth and then pulling back while making a characteristic sucking noise. It is thought to be a coping mechanism that horses develop in response to confinement or lack of stimulation. Cribbing can lead to physical issues, such as dental problems or gastrointestinal concerns, and is often seen in situations where horses are not able to express natural behaviors or are kept in restrictive environments.

In contrast, eating and grazing are normal behaviors for horses and do not typically indicate stress. Trotting is also a natural form of movement and exercise for horses rather than a sign of stress or boredom. Therefore, cribbing stands out as the behavior that signals a horse may be experiencing discomfort or a lack of engagement in its environment, making it the correct answer.