Good morning, John.

Welcome to the first episode of a new format for Bizarre Beasts, which we are calling Season zero. Over the next year, we'll be remastering the old episodes of Bizarre Beasts that I originally created for Vlogbrothers, and that means correcting stuff I got wrong the first time, updating information that's gone out of date and adding new material that did not fit in the old four minute video.

And if you didn't get a chance to get the original pin set the first time around, now you can! Stick around for those details and extra bonus facts at the end of the video. I would like to introduce you to the manul or Pallas’s cat. [♪♪INTRO♪♪] It's a wild cat that is roughly the same size as Cameo, my cat.

But while they may look similar, they are not. Spread across Tibet, China, Pakistan, India, Mongolia, Iran; these solitary, grumpy, temperamental cats eke out a living on small rodents and birds keeping warm with the longest hair of any cat, hunting hot through speed, but through stealth, with fertility windows as short as one day per year. But the thing that makes them so cute is what I want to talk about today.

Their eyes. And you may be noticing that this cutie is a little less cute than the other manuls I've showed you so far. That's because I photoshopped house cat eyes onto it.

Here's the real boy. There's something about those eyes. Just want to pause here for a sec in case you can't see the manul’s eyes for some reason - it has circular pupils, like us, not vertically slitted pupils like a house cat.

We've gotten used to the eyes of our cats, but they are a little bizarre. These vertically splinted pupils are complicated mysteries that have evolved not just in cats, but in foxes, alligators, snakes, even some birds and sharks. And not all cats have these vertical pupils.

Big cats don't have them, but most small cats do. And the lynx, which is of moderate size, actually has intermediate pupils. Or, technically, it has circular, but elongated pupils.

Animals that have vertical pupils tend to have a few things in common: they're all hunters, they all deal with low light conditions, and they're all ambush predators. But Pallas’s cat fulfills all those conditions. They’re low light ambush predators.

So how do they end up with these adorable, relatable eyes? I don't know and neither does anyone. But I found this whole thing fascinating, so let's walk through it.

There are three theories as to how vertical pupils help ambush predators. First, vertical pupils rely on a curtain of stranded muscles to contract, while circular pupils rely on a sphincter. Yes, you have sphincters in your eyes.

And that more complex musculature allows them to contract and expand more. Okay, I’m pausing here to clarify this a little. Animals with vertical pupils have both a circular sphincter and two additional muscles that compress their pupils.

So, it's still more complex musculature than we see in animals with circular pupils. Second, we have distance judgment, which is, as you might expect, pretty important for an ambush predator. And there are three ways animals use sight to tell how far away something is.

The first is parallax where objects farther away appear to move more slowly than objects close up. I'm talking specifically here about motion parallax because it's not the only type of parallax, but more importantly for the manul, ambush predators can't use motion parallax because moving their heads might give away their hiding spot to potential prey. The second is binocular stereopsis, which is the fancy way of saying normal depth perception.

When two eyes feed the brain slightly different images that are interpreted into a three-dimensional image. But last and least noticed, is blur. When you look at something, especially something fairly close up, things closer to you and farther away from you from that point appear blurry.

And when you're close to the ground, like a small cat or snake, this matters more because you're closer to your prey and thus the depth of field is shallower. The vertical pupils seem to conserve horizontal blur, which animals use as a distance judging technique, without sacrificing the vertical contrast necessary for stereopsis. Hey, me again.

We actually checked in with one of the authors of the paper I referenced here, and he put it this way: “Vertical pupils reduce horizontal blur and increase vertical blur. Animals take advantage of the reduced horizontal blur to estimate distance with stereopsis. They take advantage of greater vertical blur to use blur differences to estimate distance.

Now the third theory is a little harder to wrap your head around because it involves optics. But basically, if you want to focus on something close up with a really wide aperture, like if your pupils are super dilated because it's dark, the ability of a lens to focus kind of breaks down. Different wavelengths of light, so different colors, pass through the lens medium at different angles.

So the image will never be sharp. To get that sharp image, some animals, including cats, have actually evolved to have lenses with focal gradients. The middle optimized for green wavelengths, and then red, and then blue.

This works, but if you have a circular pupil, then when you contract, the area of the lens optimized for blue gets completely blocked. A vertical pupil on the other hand, preserves all of the color optimization. Now, as is often the case when it comes to how animals perceive the world, we're not 100% on any of these things, but we do know that with its lifestyle, a vertical pupil would be advantageous to Pallas’s cat.

So their adorable pupils, it turns out, are a mystery, an adorable mystery! They shouldn't be there, but they are. So love it.

Thank you for revisiting this beast with me. If you missed the Pallas’s cat pin the first time around, our Season Zero pin set is now available. This set includes all 12 of the animals that we began this Bizarre Beasts journey with on Vlogbrothers,

as well as a bonus pin of our very first Bizarre

Beast: The Mola Mola. Mola Mola, we're sorry that we kept you pin-less for so long! Hopefully we are making it up to you. To get the Season Zero pin set and everything else Bizarre Beasts, visit BizarreBeastsShow.com The manul is the only species in the genus Otocolobus.

Its genus name comes from the Greek words for ‘ear’ and ‘ugly.’ I'm not sure how anyone could look at these adorable grumpy little guys and go, yeah, ugly eared! But hey, I didn't name them. Their small rounded ears are probably an adaptation to the cold climates they live in.

Smaller ears mean less surface area through which to lose body heat. And while the manul is the only species in its genus, it does have other small wildcat relatives that it shared a common ancestor with sometime between 4.8 and 8.55 million years ago. These are the cats in the genus Prionailurus, which includes the rusty-spotted cat, flat-headed cat, fishing cat, and leopard cat.

These cats mostly live in the warmer, more forested parts of East and Southeast Asia. [♪♪OUTRO♪♪]