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
There is definitely also an association influencing how people view it. For example rats, people who live in cities would find rats to be gross as they are seen going into the sewers and trash and thus would have a negative association despite their intelligence. Pigs may be smart and the same with octopus and squid but how often do people actually experience that? Mostly in form of bacon and other food forms.

Dolphins and dogs both have positive associations that people experience so it’s not surprising that people would put it higher on the scale