Which of the following is a sign that a horse might be colicking?

Rolling on the ground is a classic sign of colic in horses. When a horse is experiencing abdominal pain, it may exhibit behaviors such as rolling, pawing at the ground, or frequently looking at its sides. This rolling motion is an attempt to alleviate discomfort, and it often indicates that the horse is in distress due to gastrointestinal issues.

In contrast, behaviors such as eating hay and drinking water regularly are typically signs that a horse is healthy and comfortable, as they indicate normal appetite and hydration. Whinnying softly can be a means of communication and isn't specifically indicative of colic. Therefore, rolling on the ground stands out as a key symptom that alerts horse owners and caretakers to investigate further for potential colic.