A bolt to the brain it quick and easy, they feel nothing. It’s not very dignified but neither is being eaten, that’s why we take pets to a vet is to save their “dignity”. You’re lucky vets don’t just bring your pet out back and put a bullet in its head, that’s how it used to be it changed when we started to consider pets family. All I’m saying is that a lot of humans don’t even die as quick and painlessly as cattle.