<p>Science is all about studying the world around us – from the animal kingdom to technology. To study these things, we must use our senses – like sight and touch.</p>

<p>Did you know that some creatures in the animal kingdom have things in common with U.S. currency? Both have some pretty cool special features. Here in the Science Lab, we'll find out what those special features are. You can discover them on your bills by feeling them, tilting them, and checking them with light.</p>


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<p>Well, it looks like you're pretty much an expert on how paper currency is designed now. Be sure and take a look at all the things we have talked about every time you have a bill in your hand. If your friends are around, they would probably love to hear all about the artwork on it, how it can be spent and all the science each piece of currency contains.</p>

<p>The shell of the armadillo has a unique texture – it is rough to the touch with raised bumps.</p>


<h3>Raised Texture</h3>

<p>U.S. currency also has a distinctive feel because of its special paper and the way that it's printed. If you move your fingers across the shoulders of the people on the bills, you will notice a raised texture that feels like bumps and ridges.</p>


<h3>Did you know?</h3>

<p>The human fingertip is the most sensitive part of the body. This is what allows you to feel these special bumps and ridges.</p>


<p>This is a jewel bug. But is it green or is it copper? It all depends on what angle you look at it.</p>


<h3>Color-Changing Ink</h3>

<p>U.S. currency can also look green or copper because of color-changing ink. To see the colors change, all you have to do is tilt it from side to side.</p>

<p>Color-changing ink can be seen on bills worth $10 or more. You can find the color-changing ink on the front of these bills, on the number in the lower-right corner.</p>


<p>On the $100 bill, there are actually two places where color-changing ink appears. It is both on the number in the lower-right corner and on the copper-colored inkwell. Inside the inkwell, you will see a bright green bell appear and disappear as you tilt the bill.</p>


<h3>Did you know?</h3>

<p>The human eye can see seven basic colors: red, orange, yellow, green, blue, indigo, and violet. This is also called the "The Color Spectrum."</p>


<p>Many animals have patterns on their skin. The cuttlefish can create any pattern it wants and can even make them move.</p>


<h3>3-D Ribbon</h3>

<p>$100 bills have a special pattern on it's 3-D Ribbon. When you tilt it in different directions, the pattern will move and change. The images on the ribbon are bells and little "100's".</p>


<p>Some jellyfish are actually hiding a secret. Take a look at this one against the light – you can see a school of fish hiding under its bell.</p>


<h3>Watermarks</h3>

<p>U.S. currency also hides some secrets! All bills with a value over $5 have secret, hidden pictures on them that you can see if you hold a bill up to the light. These hidden pictures are called watermarks.</p>

<p class="did_you_know">A watermark on a bill is usually the head of the person on the bill. But on the $5 bill, it is a number. These watermark numbers are on both sides of the bill.</p>


<h3>Special Thread</h3>

<p>When you also hold U.S. currency up to light, you'll also see a special thread hidden inside (in bills with a value of $5 or more). The thread is a narrow strip running up and down the bill. You can see it from both the front and back sides.</p>


<p>This millipede looks normal until you hold it under an ultraviolet, or UV, light. Then it glows brilliantly.</p>


<h3>Watch: You'd Be Surprised Special Features</h3>

<p>Now let's watch a video that brings to life all the cool creatures and features you just learned about.</p>
