Mark Twain once wrote, "You can't depend on your eyes on your mind is out of focus." While it's from his book, "A Connecticut Yankee in King Arthur's Court," it always reminds me of those crazy images that play tricks with your mind.

Don't know what I'm talking about? Perhaps this will jog your memory.

I don't know why, but I've always found these really interesting. How your mind can make connections and see things that aren't really there is so cool. I've picked out some of my recent favorites to share with everyone!

1. Checker shadow illusion.

The A and B tile may look like they're different colors — but they're actually the exact same! Don't believe it? Neither did I until I cut them both out and in paint and put them next to each other. This was first published by MIT Professor Edward H. Adelson in 1995.

2. The Ponzo illusion.

Even though it doesn't look like it, all three cars are in fact the same size. It's called the Ponzo illusion and works because our brain judges an object’s size based its perceived distance.

3. Look at yellow dot, move your head further and closer.

I can't find much about what this is called, or why it works — but it's trippy as can be, and works really well. One ring appears to move clockwise while the other moves counter-clockwise depending if you're moving closer or further from the screen.

4. Light to dark.

Similar to the last one, you want to look at the center of the image and slowly move toward or away from the screen. Moving towards the screen the image appears to get brighter, while if you move away it looks like it's getting darker.

5. Color me surprised.

Your mind is able to fill in what colors should be where by staring at the inverted color scheme.

6. Scintillating grid illusion.

I swear this isn't a gif file. When focusing attention on a single white dot, some grey dots nearby and some black dots a little further away also seem to appear, although all the dots are really white. Cover some up with your hand check for yourself.

7. The .jpg image that looks like a .gif image.

Like the others that look like a moving image, this is yet another plain photo that looks like it's rotating.

8. You're the conductor here.

Is this train going in the tunnel, or out? The gif is only a few frame long, your eyes and brain are trying to fill in the answer and tend to switch every now and then.

9. Spinning dancer.

Similar to the last one, you're in control here. If you look at the dancer on the right first then the center, she appears to be rotating clockwise. But if you look at the one of the right then the center she looks like she's spinning counter-clockwise. This was designed web-designer Nobuyuki Kayahara.

10. Crossing circles.

These circles are made of squares and look like they're all knotted and overlap--but not a single square is touching another. Trace each circle with your mouse or finger. It's wild.

11. 12 dots, but you can't see them all.

I don't know why but your brain won't let you see all 12 dots at once... and I don't know if it's an actual illusion or my eyes just messing with 'em after looking at these kind of things all day, but I also see white squares where the grey lines intersect.