Who got a good whiff of say your new date and started snarling at him, who indeed turned out to be a jerk or something?
I have cats. I’m not 100% sure on a day-to-day basis if they’re evil or not. So they could love someone who is equally evil. 
More seriously though, no, one of my cats is so-food driven that Beelzebub themselves could show up and get love and affection as long as they brought a bag of Greenies. And my other cat loves pretty much everyone who pays attention to them. Which won’t stop him from clawing the hell of said person once they hit the stimulated level.
And the snake, well, snakes don’t care.
We had a Siamese cat who took a strong dislike to one of our acquaintances who turned out to be a real scumbag. She would follow him around the house and sit near him, staring fixedly at him. Aside from that, though, we don’t typically have evil people over, so it’s hard to say whether our current cats would spot one.
Danger-Detecting Pet?
Our first dog, the Border Collie, detected a fire breaking out in the ductwork of a house we were renting. She stood there, snout pointing at the source of ignition (behind the wall, yet) until the firemen came with their hot-spot detector device and declared all’s well. Swear to Frith!
(A piece of insulation had sparked from one of the coils and floated up the duct and snagged on that spot. It, possibly, could have been serious. Mucho treats and Good dog! was her reward.)
I once had a cat that didn’t like the man I was dating at the time. She was right (although it was my fault, too).
My first cat Simba loved my first girlfriend, Dana. She turned out to be a little shit. So no, my cats are 0-for-1.
We were having a party at my house in 1972, there must have been about 50 quests. I had a very well trained German Shorthaired pointer and I brought him in the house to show him off a little. He was doing fine and suddenly locked eyes with my wife’s girlfriends’ new boyfriend. It took everything I had to restrain the dog and get him outside and back in his kennel. He wanted to kill this guy. We later found out he was a fugitive from New York wanted for killing his girlfriend.
Yeah, we had a shetland sheepdog like that.
Then I have a husky who would happily lead the burglar to the valuables.
Detecting evil? No. Evil? More than one.
My Siamese cats hate everyone and most things invading their lives. Including me, on occasion.
Bayliss, the tail-less, the fearless, the peerless is very vigilant. He scans and computes everyone coming through this house. He’s had one bad reaction to a guy Son-of-a-wrek brought around.
I’ve had my ears and eyes open, so far nothing has turned up about the guy.
I told Son to just wait. Something was bad about him. And not to bring him around again.
CeltDog is the lovingest little dog you could ever hope to meet. But we had a neighbor once whom he absolutely hated. I took his advice. I’ve never heard anything to confirm his opinion, but I trust to this day that I did the right thing in believing him.
On the other side of the coin, I don’t think I’m evil (though opinions may vary). But several times in the past, unfamiliar dogs who seemed friendly to others have taken a strong dislike to me. Mrs. solost has even joked about it in the past. She used to volunteer at an animal shelter, and she’d work adoption events, where they’d display adoptable animals at public places like the local zoo. The kids and I would go visit, and I remember one dog in a cage (which she said was very friendly otherwise) would go nuts whenever I’d go up to the cage and try to talk to it, barking and snapping at me.
Maybe it’s because I was mauled by a German Shepherd when I was 6, so I have a subtle skittishness around dogs that they pick up on. Or maybe I’m a latent evil maniac, and I’m hiding it well, even from myself.
Our Max (dachshund) used to always bark at Louie – our neighbor in the townhouse across from ours. Even after he’d (Max, not Louie) warmed up to all our other neighbors, he’d still always bark at Louie. No, Louie is a nice guy (as is his wife), so I’m thinking it was a territorial issue. Louie was just too close, and Max was warning him to keep his distance.
Never had a pet spot someone actually evil.
Our labs love everyone. I’m sure if Dahmer, Hitler, Stalin walked in and gave them pets, they’d find them delightful.
Social animals, like humans, can sense signs of aggression (even subtle ones) from others. This skill helps them survive in the wild. Evil people who treat other people badly often treat animals badly too, even if they don’t outwardly show it. Evil people also often have loud and harsh voices—which animals don’t like. A loud sinister laugh will set your pet on high alert.
Some signs that someone is not friendly to animals are ignoring them, avoiding eye contact, or speaking in a cold tone. And, when they kick your poor kitty or pup while you’re in the bathroom, well that’s a clear sign of overt aggression which your pet will remember and plan on avenging justice.
Most pets also care about you, their owner. So, they notice when someone is being mean to you too.
I’ve had a lot of pets throughout my life (cats, dogs, and other social animals). And most of them were good at reading people’s intentions and acting accordingly.
Currently, my cat Benny (one of my clowder of 5) is the most sensitive to evil intentions. He protects me from human evil-doers and I protect him from Meatball, the bully cat.
My Reese mostly was wary of anyone. It was more that he would detect people who were nice and, above all, calm.
I had a cat that loved everything and everybody, and my brother had a cat that hated everything and everybody. They met when we were at our parents’ place for Christmas, and the instant I opened my cat’s carrier, she folded her ears back and hissed at him. They had to be kept in separate rooms the whole time we were there.
When they had their first child, one thing they got at the baby shower was a memory book, and one of my SIL’s sisters said, when she saw the “My Pets” page, “You’re not going to put Al’s name in this thing, are you?” He found the pregnancy and the new baby quite interesting, until she was about 3 weeks old and he realized that not only was that THING getting bigger every day, it wasn’t going to be leaving any time soon. Among other things, he threw up on their bed, and they just knew he did it on purpose. When they had their second child a year and a half later, his attitude was, “Oh, great, another one of these.” He went over the Rainbow Bridge when they were preschoolers, but they do remember him.
I’ve always wondered if the cats owned by Amy of Amy’s Baking Company/Gordon Ramsay notoriety felt affection for Amy. If they did, that strongly suggests that cats are useless at sniffing out at least certain kinds of evil.
My Rat Terrier hated my Daddy.
He said, when he saw her the first time, “Are you sure that’s a dog?”
She never forgave him.
He had dogs. My other dogs knew him. He never had a problem.
He tried bringing her snacks when he came to visit. No dice. She never warmed up.
He wasn’t evil. He was a bit loud and moved around too much for her tastes. I guess.
Did other people bring her dice?