system
A chat on subreddit /r/NoStupidQuestions
human
Yet octopus and squid are fair game despite them being one of the most intelligent creatures on the planet.

Pig is fair game despite being smarter than dogs and biologically similar to people to the point we practice anatomy on them.

Rats and mice are fair game despite being so intelligent we use them in studies to analogue human behaviour. 

I honestly think it's about how endearing our culture views an animal. Rats and mice are "icky" pigs are "dirty" and things with tentacles are "weird". But deer and bear are like Bambi and Smokey.
gpt
I think it is also important to consider that dogs have co-evolved with human for 10,000 years, more than twice as long as any other domesticated species. It is likely that dogs are much better at understanding emotion of humans and provide comfort to them (since we bred them for that for 100 centuries). A pig or a squid might be more intelligent on paper, but they can never interact with humans like dogs, so we are less likely to feel sympathy to them.