An alternative grip for controlling pit vipers is the three fingered head grip depicted in this photo of a Wagler's temple viper (Tropidolaemus wagleri). This grip is not as strong or secure as the two fingered hold, and if your top finger slips it will be immediately in fang range.
One finger rests on the back of the animal's head. The thumb and the middle finger are kept tight to the mandible (the back of the jaw) and care is taken to keep fingers far enough back that they are out of fang range. The configuration is similar to the two fingered head grip, except that the middle finger is used in place of the first finger.
A really determined pit viper can snap its fangs out while its mouth is closed, or put a fang through its own lower jaw to bite a handler. It is a good idea to keep your fingers as far back as possible on the neck while maintaining a secure grip.
A second hand is always necessary to help control and support the body. Pit vipers are physically fragile and the single occipital condyle that connects the skull to the spine can easily be dislocated by the animal's body weight if it struggles while its head alone is restrained. A strong enough animal can thrash its way out of an unsupported one-handed grip and cause injury to its handler as well as itself in the process. It is a good idea to utilize tubes for better control and restraint. Because this direct grip on a snake's neck is risky for both the snake and the handler, it should be avoided unless specifically necessary during a veterinary or scientific procedure.
What might be wrong with the situation depicted in this photo? Because of the medication being applied to this animal's extensive epidermal lesions (Thermazine/silver sulfadiazine for suspected necrotizing dermatitis), the handler's grip may be slippery and thus less safe. If this animal had been physically stronger and more alert, a much safer alternative for applying this medication would have been with a long swab while the animal was restrained in a tube. Chemical restraint (anesthesia) is also a humane option for dangerously aggressive patients that require extensive manual procedures which may put both the animal and the handler at risk.
However this was an extremely weak and debilitated animal with a protozoal infection (Entamoeba invadens) which had caused significant damage to the GI tract. The petechiations on its ventral aspect were probably indicative of a generalized bacterial septicaemia rather than a surface process. Ventral petechiations (typically small brown, pink or red lesions on and between the scales) can be indicative either of a bacterial or fungal problem on the skin or a much more serious systemic infection. This particular animal could be effectively restrained with very little effort due to its weakened condition. This is certainly not the case with all venomous reptile patients, so it's a good habit to make sure your hands and the snake's neck are not slippery with medication while you are handling.