He Jen is holding the head and front legs so a technician can try to obtain blood from its neck. Ferrets' skin is usually thick and sometimes they are hard to obtain blood this way. Sometimes we are required to place the animal on their backs to get blood from them. Grabbing ferrets by the scruff of the neck has a tranquilizing effect on them. By doing so we are allowed to clip nails, clean ears and exam the animal.
Birds are quite agile as well.
They usually never go where you want them to. They usually insist on pearching on your shoulder instead. Dr. V, has grasped her bird firmly here. She has control of the head and neck so the bird is unable to move its head to nip at anyone. When clipping nails, wings or grinding beak it is important to have a firm grip in the bird's head.