Which of the following is a method of mechanical restraint?

A head snare is recognized as a method of mechanical restraint because it involves the use of a physical device specifically designed to control or limit an animal's movement. Mechanical restraints are tools or devices that apply physical force to restrict an animal's ability to move freely. Using a head snare is an example of this because it physically captures and holds the animal's head in place, preventing it from moving or escaping.

In contrast, gentle holding is a form of physical restraint but is often more about using body contact and less about employing a mechanical device. Verbal commands and calming sprays are behavioral methods that do not involve physical restraint; they aim to influence an animal’s behavior through communication or chemical means, respectively. Thus, the only option that fits the definition of a mechanical restraint is the head snare.