The imagination of man to perform evil seems limitless; c.f. the Indians of the Ohio River Valley and the Toronto area of Canada with their torture methods. The Hurons were so called because that is a derivation of the French word for “the rough ones.”

LD50 is something, but what’s the lethal dose for 0.01%?

Orally, potassium chloride is toxic in excess; the LD₅₀ is around 2.5 g/kg (meaning that a lethal dose for 50% of people weighing 75 kg (165 lb) is about 190 g (6.7 ounces)). However, this is not far from oral toxicity of sodium chloride (table salt), of 3.75 g/kg, thus potassium chloride is harmless for alimentation (and even good for health, see previous paragraph). But intravenously, without the step of digestive absorption, this is reduced to just over 30 mg/kg.

Pets are almost always euthanized by intravenous injection, typically using a very high dose of pentobarbital or sodium thiopental. Unconsciousness, respiratory then cardiac arrest follow rapidly, usually within 30 seconds. Observers generally describe the method as leading to a quick and peaceful death.

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Some veterinarians perform a two-stage process: an initial injection that simply renders the pet unconscious and a second shot that causes death. This allows the owner the chance to say goodbye to a live pet without their emotions stressing the pet. It also greatly mitigates any tendency toward spasm and other involuntary movement which tends to increase the emotional upset that the pet’s owner experiences.

For large animals, the volumes of barbiturates required are considered by some to be impractical, although this is standard practice in the United States. For horses and cattle, other drugs may be available. Some specially formulated combination products are available, such as Somulose (Secobarbital/Cinchocaine) and Tributame (Embutramide/Chloroquine/Lidocaine), which cause deep unconsciousness and cardiac arrest independently with a lower volume of injection, thus making the process faster, safer, and more effective.

Occasionally, a horse injected with these mixtures may display apparent seizure activity before death. This may be due to premature cardiac arrest. However, if normal precautions (e.g., sedation with detomidine) are taken, this is rarely a problem. Anecdotal reports that long term use of phenylbutazone increase the risk of this reaction are unverified.

After the animal has expired, it is not uncommon for the body to have posthumous body jerks, or for the animal to have a sudden bladder outburst. Unlike in films, the animal’s eyes do not usually close when it dies, and this has been stated purely as a drama display for pet death in movies (such as Marley & Me).