system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are venomous mammals and birds so rare in comparison to reptiles and fish?

Venomous species are hard to find in mammals, even more so among birds. What's the deal with all these venomous snakes, lizards, and fish?
gpt
sadly this is something that an ELI5 probably can't answer because it's something not a lot biologists have a good answer for. some suspect it's because claws and teeth are just much faster easier way of killing things course then the question is why don't insects,fish,and snakes use their teeth and claws more. 

it may well be that the evolutionary line which produced placental mammals just happened to not be amongst the reptiles which have venom relegating it to marsupials and those with errant mutations in their digestive enzymes.

but there really isn't a lot of good information on why venom is so rare in mammals.