Or take this image:

Oyvind Kolas

That is a black-and-white photo with some colored lines laid on top, but you perceive colored clothes, colored seats, etc. If you look closely at any one small part, you will correctly note the gray image and the colored lines, but everything outside your fovea's range is a blur, so your brain mashes it all together. The tiny size of the fovea is also responsible for a lot of classic optical illusions. There's some debate among eye scientists about precisely why it is that you see imaginary gray circles in the intersections of this grid:

Wikipedia

But you sure don't see any in the specific intersection you're focusing on. You can read designer Yurii Perepadia's explanation for what's going on with all this brain-teasing mind sorcery, but the relevant part for us right now is that you perceive whichever part you're focusing on correctly. Everything else is outside your fovea, and is thus total guesswork.

Related: 5 Optical Illusions That Prove You Can't Trust Your Own Mind

But way weirder than the psychology of taste is what happens when individual types of taste buds get switched off and everything suddenly gets screwy. That awful taste when you drink orange juice after brushing your teeth? That's not because of the aftereffects of mint; it's because the soapy chemicals in toothpaste numb your sweet taste buds and prime your bitter taste buds by dissolving their fatty coating. For a switch that's similarly weird but a lot more pleasant, try eating an artichoke and then drinking water. A chemical in artichoke called cynarin coats your sweet receptors. When you drink water, the chemical is washed away, stimulating them, and you feel like you're consuming something sweet, even though you're not.

So you can turn sour to bitter and water to candy. You can also get fooled into thinking sour things are sweet using a weird fruit called Synsepalum dulcificum (or by buying its extract online, if you're unfortunate enough not to live where it's cultivated in Taiwan or West Africa). Eating "miracle fruit" coats your sweet receptors ... until acid activates them. So pop a little dulcificum, and for the next half hour, lemon slices will taste like gummy worms. Now lean back and laugh at your taste buds detecting legitimate nutrition as you shotgun an entire bottle of soy sauce.

Related: 5 Mind-Blowing Ways Your Sense Lie To You Every Day

There are a few exceptions where we instinctively absolutely hate certain smells -- like cadaverine and putrescine, which are related to rotting and corpses. But it's when we try to identify and measure these aversions that things get really weird. Take, say, poop. It smells how it does largely because of an organic compound called indole. And yet some flowers, like jasmine and orange blossoms, also produce indole. When perfumes want to smell like flowers, they almost always include some indole. And this makes them smell good, even though they technically smell like s**t.

That's not the only chemical that confuses the nose like that. P-cresol is another compound that forms in the large intestine. It's what makes farm animals smell bad, and scientists have set up experiments detecting the concentrations of p-cresol downwind of farms to try to measure how odors spread. But the compound is also added to perfumes. In this case, it only smells bad at low concentrations, such as when it's dispersed through the air and goes into your open car window when you're driving by that herd of cows. But when super concentrated, p-cresol smells medicine-y, like Lysol.

Basically, what I'm trying to say is that if they developed a perfume that was pig-ass-themed, it would smell heavenly.

Related: 20 Ways Your Perception Gets Screwed Up By Your Brain

Now take the cold coins out and lay them on either side of the third. Touch your pointer finger to the top of one of the cold coins and your ring finger to the other. Now touch the middle coin with your middle finger. It feels cold too, even though it isn't. And it's not that your fingers just feel cold all over; your middle finger doesn't feel cold until it makes contact with the third coin, and your brain gets all those signals and figures that third coin has to be cold too, because that's the only thing that makes sense.

Your fingers are very sensitive to touch (as can be tested, very easily, by firing lasers at them, or by seeing how much more painful it is to slam your fingers in a door than to slam your whole arm), which has been pretty useful when we've had to learn to use tools and write and stuff. It's just that fingers aren't always so great at working individually and figuring things out correctly.

Now if you REALLY want to spook yourself, you can try a similar thing with your nose. Cross your left middle and index fingers and touch the V formed at the end to the bridge of your nose, while closing your eyes. You may suddenly feel like you have two noses. According to an expert, "the nose is not the only appendage in which perceptual doubling can be produced." Which is a coded way of stating that a scientist who tested this then immediately tried the same thing on his penis, because of course he did.

Related: 5 Ways Your Brain Is Messing With Your Head

But even if sound vanishes at points, your brain fills in the blanks and lets you understand it through a process called phonemic restoration. This video shows what's going on:

You will hear lines of speech with every other beat removed, rendering it seemingly unintelligible. But when a sort of neutral static ("pink noise") is laid over the whole thing, you'll suddenly be able to understand the lines, even though none of the missing parts have been put back in. Your brain does this often without you realizing it, because all kinds of background noises are forever interrupting all of the important hot takes we're trying to tell people.

Plenty of what you think you hear is also affected by your memories. The music in the following video is played entirely using a (computer-simulated) piano. It plays nothing but notes. But hearing so many familiar details from the song "Stayin' Alive," you will swear that you can hear lyrics, which exist nowhere but in your own head. So bad news: It makes you feel a little crazy. But good news: We're all crazy.

And a lot of the time, you use context to figure out what you're hearing. This next video is the "bill bill bill" refrain from the Bill Nye theme song over and over, but as the images change, the sound seems to shift to "bale," then "pail," and then, weirdest of all, "mayo":

For the sake of completion, you should now listen to a 10-hour video of "Bill Bill Bill" to hear how the sounds change over time. I'll wait here patiently until you're done.

Follow Ryan Menezes on Twitter for bits cut from this article and other stuff no one should see.

For more, check out The Eyes Have It - Does Not Compute:

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