Some of the commonly used methods for euthanasia are: 1. Injection of a barbiturate anesthetic, which causes the animal to become unconscious and then stops the heart and breathing. This is considered the most humane and painless method. 2. Inhalant anesthetics, such as carbon dioxide or carbon monoxide, which cause the animal to become unconscious and then stop breathing. This method may be used for smaller animals or in emergency situations where injectable anesthetics are not available. 3. Physical methods, such as cervical dislocation or decapitation, which cause immediate death but may be considered less humane and more distressing for the animal. Please remember, euthanasia should only be performed by a licensed veterinarian or a trained professional and should always prioritize the welfare and comfort of the animal.