Practice Relating to Rule 70. Weapons of a Nature to Cause Superfluous Injury or Unnecessary Suffering
Mexico’s Army and Air Force Manual (2009) states:
The underlying idea of this body of law [i.e. IHL] is to humanize war. The three main principles established to this end … [include]:
B. all means of warfare that may cause superfluous injury or unnecessary suffering, that is, means of warfare not essential to defeating the enemy, are prohibited.
In a section entitled “Basic rules of international humanitarian law applicable in armed conflicts”, the manual also states:
Parties to a conflict and members of their armed forces do not have an unlimited choice of methods and means of warfare. It is prohibited to employ weapons or methods of warfare that can cause unnecessary losses or excessive suffering.
In 1974, during discussions in the Ad Hoc Committee on Conventional Weapons established by the CDDH, Mexico stated:
The debates in the United Nations General Assembly which culminated in the approval by an overwhelming majority of resolution 3076 (XXVIII) relating to napalm and other incendiary weapons were eloquent proof that humanity was anxious for the prohibition of the use of those weapons as well as other conventional weapons which could be considered as causing unnecessary suffering.
In 1976, during discussions on napalm and other incendiary weapons in the Ad Hoc Committee on Conventional Weapons established by the CDDH, Mexico stated: “Incendiary weapons … were cruel weapons which caused unnecessary suffering, especially to those with least protection, namely, innocent victims not participating in military operations.”
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, Mexico affirmed:
72. The  Declaration of Saint Petersburg was followed by a series of international instruments in which the idea of preventing unnecessary suffering and superfluous damage to the enemy led to a prohibition on the use of certain weapons. Such instruments included The Hague Conventions of 1899 and 1907, which prohibited the use of poisoned or poisonous weapons and or arms, projectiles or materials causing unnecessary suffering; the …  Geneva Gas Protocol … and the [1972 Biological Weapons Convention] … etc.
73. … All the above-mentioned instruments have made it clear that the right of the parties in an armed conflict to choose the means of harming the enemy is not unlimited and is, in fact, subject to restrictions. In this regard, it is worth highlighting Article 35 [of the 1977 Additional Protocol I] … which reaffirms that the right of the Parties to an armed conflict to choose methods or means of warfare is not unlimited and that it is prohibited to employ weapons, projectiles and material and methods of warfare of a nature to cause superfluous injury or unnecessary suffering.
75. The international community considers that certain types of armaments should be prohibited on account of their inhumane effects on individuals.