Answered by Ustadh Salman Younas
Question: I own snakes and feed them live rats. Feeding live rats is very dangerous for the snakes because the rats tend to fight back. What is a permissible way to kill the rats?
Some people slam the rats. Some people put the rats in a container and leak in CO2 to put them to sleep and then kill them.
Answer: assalamu alaykum
The Prophet (blessings and peace be upon him) forbade making animals suffers as related from Abu Hurayra by al-Bukhari. Due to this, Ibn Hajar al-Haytami listed hitting animals in a painful manner without a sound reasons to be a major sin. [Ibn Hajar, al-Zawajir (2:140)]
You should certainly avoid slamming the rats to kill them as this is clearly problematic. The CO2 method that you mention seems less painful and is the method approved by the American Veterinary Medical Association. If you are able to utilize it soundly, it should be given preference over the other one you mention.
I am unsure of other methods given my lack of experience in the area. The upshot, however, is that you should take all reasonable means to ensure that the animal is killed in a manner causing the least amount of harm.
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