Ran

Haven’t drawn this guy in like,,, actual 3 years wowz

Doctor kind of just looks at his agent and forms a hypothesis that, with all kinds of things Stone is capable of doing and tolerating(maintaining his calmness and a somewhat good mood after being around Robotnik for a long period of time included), he simply cannot be human. Doctor doesn't know what he is, but he doesn't doubt his theory.

In fact, being a man of science that he is, Robotnik goes on to scientifically prove it(to which Stone, the ever loyal agent, agrees to), quite literally putting the man under a microscope, just to find out that.. he is, in fact, a human.

Now, he's certainly disappointed — finding a sentient alien of sorts would have been thrilling — but mostly just appalled. So he all but inspects Stone, thoroughly, to find out if there's anything extraordinary about the man's body or brain. He's almost offended to see that, despite being just a few screws loose in the head, Stone is a completely ordinary, imperfect human. There's absolutely no reason for him to be able — or willing to — go through everything he'd been through, and yet here he is.

Harpies who can't write or type or open most containers with their wings. Werewolves who worry about hurting someone if they get overstimulated at the wrong time. Minotaurs with digestive systems and metabolisms which require grazing throughout the day, not the three big meals humans are used to.

Lamias who have to stay home in the evenings and during cold months to stay warm, otherwise their muscles stop working right and they get stranded. And they're sick of their human friends suggesting they get some kind of tail sweater. It wouldn't help, the problem is that their body doesn't produce enough heat to begin with, and anyways a tail garment would get in the way of their rectilinear locomotion, and there's no way a sweater would survive being walked on in the first place. It feels like they don't actually care about you being stuck at home whenever they go out, they just want to feel like it's not their fault they never see you.