You can mix vinegar (or some other mild acid like lemon juice) with baking soda in a jar or bottle to make carbon dioxide gas. since carbon dioxide gas is heavier than air, put your prey animal in a sealable container with a tight lid, and "pour" the gas into it and close it up tight. the animal will die or at least be stunned long enough to safely feed it to your snake. make sure you have a batch of gas big enough to fill the container, though. an animal asphyxiating slowly is not a pretty sight or sound.