Evidence shows that fish are just as smart as birds and mammals. According to studies, they can even remember things for three to five months.
Most dogs do not brush their teeth twice a day or floss, so no, their mouths are not cleaner than ours. You won't find humans eating trash or licking out of toilet bowls, either. It is true, however, that the healthier the dog, the cleaner they are. It's believed that this myth comes from the fact that dogs' wounds heal after they lick them. It's not their mouths are especially clean, it's just a similar practice to us washing a wound to prevent infection.
Contrary to what you were probably taught in elementary school, Christopher Columbus was apparently smarter than what we give him credit for. The Italian explorer knew the world was round even before embarking on his expedition. The fact that the world was a sphere was actually known 1,300 years before Columbus set sail, but it is true that many Europeans did start to believe the flat rumors during the Middle Ages.
You may have heard that Newton discovered the law of gravity one day when he was sitting beneath an apple tree, which is somewhat true. An apple was involved, but the revelation didn't come to him because of one hitting him on the head. He did see one fall from a tree, which made him wonder why apples fall straight to the ground instead of sideways. It's still a cool story, though.
The real reason chameleons change color is to control their body temperature and to express mood. Cool, huh? As you can guess, darker colors absorb more light, so they'll swap to a lighter color to stay cool. In terms of emotion, they'll darken their shade when they're scared and brighten when they're excited.
