Your body is truly a wonderland (thanks for the line John Mayer).

Human biology is so unbelievably complex that scientists still make unbelievable discoveries every year. Some things are still mysteries, but what we do know is pretty incredible.

For instance:

1. The human eye is (technically) capable of seeing ultraviolet light.

Under standard conditions, ultraviolet light is invisible—we can’t see that part of the spectrum, since the eye’s lens filters out those potentially harmful wavelengths. Remove the lens, however, and that could change.

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That’s exactly what happened to the great painter Claude Monet, who developed cataracts late in life. As Carl Zimmer wrote:

“As [Monet’s] lenses degraded, they blocked parts of the visible spectrum, and the colors he perceived grew muddy. Monet’s cataracts left him struggling to paint; he complained to friends that he felt as if he saw everything in a fog.” “After years of failed treatments, he agreed at age 82 to have the lens of his left eye completely removed. Light could now stream through the opening unimpeded. Monet could now see familiar colors again. And he could also see colors he had never seen before. Monet began to see–and to paint–in ultraviolet.”

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Here’s another cool (and slightly disgusting) eye fact: Millions of people have eyelid mites, which feed on old skin cells. In small numbers, they’re harmless, but they can cause irritation and redness if you get too many in one area.

2. Your brain knows where you’re going to move (before you’re aware that you’ve decided to move).

Stay with us, here. A 2015 study found that the human brain plans out movements before deciding to make those movements.

A research team led by Karel Svoboda studied the premotor cortex in humans and animals. This part of the brain determines movement but doesn’t receive sensory input.

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“You can actually read out from the neurons what the animal will do in the future,” he says. “In humans, you can record this activity with an EEG electrode and read out in coarse terms when and how a person will move, before he or she is aware of where they will move.” In other words, your brain knows that you’re going to move before you do. Try not to think too hard about that one.

3. Your brain controls every organ system—except your gut.

Maybe that’s why “thinking with your gut” is such a popular expression. Your gut has over 100 million neurons—brain cells—and it’s capable of sending emotional signals to your brain.

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Of course, it doesn’t work all on its own; a healthy human has trillions of bacteria living in the gut biome. These microorganisms kill invading pathogens, help you process food, and even restore the gut to its original pristine condition while you’re recovering from illness.

4. Your bones are stronger than steel.

In fact, bone is five times stronger than steel. It’s also much lighter, making up a mere 1/6 of your body’s total weight, and it’s not exactly impact-resistant.

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Oh, and you lose bones as you age. Babies are born with more than 300 bone structures (including some made mainly of cartilage), but adults have a mere 206.