What made Geralt realise that Vereena wasn't a rusalka but actually a vampire?

Question

In The Last Wish shortly after leaving Nivellen Geralt pulls up to a stream to let Roach have a drink. Whilst drinking Roach backs away from the stream at the sight of "an ordinary devil's ring".

About midday, while Roach was drinking at a spring, the mare neighed piercingly and backed away, baring her yellow teeth and chewing her bit. Geralt calmed her with the Sign. Then he noticed a regular ring formed by the caps of reddish mushrooms peering from the moss.

“You're becoming a real hysteric, Roach,” he said. “This is just an ordinary devil's ring. What's the fuss?”

The mare snorted, turning her head toward him. The witcher rubbed his forehead, frowned and grew thoughtful. Then he leapt into the saddle, turned the horse around and started back, following his own tracks.

“Animals like me,” he muttered. “Sorry, Roach. It turns out you've got more brains than me!”

_{The Last Wish, "A Grain of Truth" IV}

Geralt recites "Animals like me" after what Nivellen had told him shortly before leaving and turns back to go to the mansion.

“Animals like me,” boasted the monster. “And I like them, too. My cat, Glutton, ran away at the beginning but she came back later. For a long time, she was the only living creature who kept me company in my misfortune. Vereena, too—” He broke off with a grimace.

Geralt smiled. “Does she like cats too?”

“Birds.” Nivellen bared his teeth. “I gave myself away, pox on it. But what's the harm. She isn't another merchant's daughter, Geralt, or another attempt to find a grain of truth in old folk tales. It's serious. We love each other. If you laugh, I’ll sock you one.” Geralt didn't laugh. “You know your Vereena,” he said, “is probably a rusalka?”

_{The Last Wish, "A Grain of Truth" II}

This all connects together when Geralt confronts Vereena and works out she is a bruxa, a type of vampire.

“You're so like a rusalka,” the witcher continued calmly, “that you could deceive anyone. All the more as you're a rare bird, black-haired one. But horses are never mistaken. They recognize creatures like you instinctively and perfectly. What are you? I think you're a moola, or an alpor. An ordinary vampire couldn't come out in the sun.”

[...]

The witcher backed away and clasped the hilt of his sword tighter. “That means you're—”

The corners of the lips started to turn up higher and higher; the lips flew open…

“A bruxa!” the witcher shouted, throwing himself toward the fountain.

_{The Last Wish, "A Grain of Truth" V}

This all makes some sort of sense in connecting together but I can't really fit all the pieces together.

• Why did Roach's reaction to the "ordinary devil's ring" make Geralt realise Vereena wasn't a rusalka?

• What does "animals like me" have to do with it?

• The connection with birds seems to be that as a vampire she has a bat form but I'm not 100% sure.

In short, what made Geralt realise that Vereena wasn't a rusulka but actually a vampire?

Answer 1

I think I've worked it out, Roach's reaction to the "ordinary devil's ring" is nothing special it's just that Roach reacts which jogs Geralt's memory and makes him realise what had happened. He remembers that Roach was uneasy when near Vereena before entering the mansion and then when entering the mansion.

The mare tossed her head, neighed wildly, stamped and danced on the path, kicking up a storm of dried leaves. Geralt, wrapping his left arm around the horse's neck, swept his right hand—the fingers arranged in the Sign of Axia—over the mount's head as he whispered an incantation.

[...]

A girl was standing on the slope of the hill he had just climbed down, one arm resting on the trunk of an alder tree. Her trailing white dress contrasted with the glossy blackness of her disheveled hair, falling to her shoulders. She seemed to be smiling, but she was too far away to be sure.

[...]

Roach neighed anxiously, tossing her head. Geralt, still watching the forest, instinctively calmed her with the Sign again. Pulling the mare by the bridle, he walked slowly along the wall, wading through burdock up to the waist.

He came to a sturdy gate, with iron fittings and rusty hinges, furnished with a great brass knocker. After a moment's hesitation Geralt reached out and touched the tarnished ring. He immediately jumped back as, at that moment, the gate opened, squeaking, clattering, and raking aside clumps of grass, stones and branches. There was no one behind it—the witcher could only see a deserted courtyard, neglected and overgrown with nettles. He entered, leading Roach. The mare, still stunned by the Sign, didn't resist, but she moved stiffly and hesitantly after him.

_{The Last Wish, "A Grain of Truth" II}

However, this couldn't have been because of Nivellen as "animals like me" and so something else had to have spooked her. And if Vereena was truly a rusalka Roach probably wouldn't have spooked as much so there was something more to her.

He was also probably still wondering about the corpses he had found in the forest beforehand who had died due to "blows to the neck".

The woman in the sheepskin and blue dress had no face or throat, and most of her left thigh had gone. The witcher, not leaning over, walked by her.

The man lay with his face to the ground. Geralt didn't turn the body over, seeing that the wolves and birds hadn't been idle. And there was no need to examine the corpse in detail—the shoulders and back of the woollen doublet were covered with thick black rivulets of dried blood. It was clear the man had died from a blow to the neck, and the wolves had only found the body afterward.

_{The Last Wish, "A Grain of Truth" I}

It is only as Geralt is leaving that Nivellen tells him that the two had been there at the mansion previously and so he didn't really have time, or want to question them on it.

“I’m not as stupid as you think. You came here following the tracks of one of the merchants who'd been here lately. Has something happened to one of them?”

“Yes.”

“The last was here three days ago. With his daughter, not one of the prettiest, by the way. I commanded the house to close all its doors and shutters and give no sign of life. They wandered around the courtyard and left. The girl picked a rose from my aunt's rosebush and pinned it to her dress. Look for them somewhere else. But be careful; this is a horrible area. I told you that the forest isn't the safest of places at night. Ugly things are heard and seen.”

_{The Last Wish, "A Grain of Truth" II}

And so remembering Roach being scared and the corpses who died to neck wounds he put two and two together to realise that Vereena was a vampire. The "ordinary devil's ring" might not mean anything specific but vampires are often coupled with the devil and so that might have helped Geralt make the connection.