Camera flashes do not make your eyes turn red. The inside of your eyes are always red. The bright light of the camera flash just makes the color more obvious. Your eye is essentially a hollow ball filled with clear fluid. The hole at the front of your eye, the pupil, lets light into the hollow space inside the eye. The light passes through this space and then strikes the inner back surface of the eye, known as the retina. The retina is packed with cells that detect the light, change it to electrical signals, and pass the signals on to the brain where the pattern of light is experienced as a visual image. The approximately 100 million light-sensitive cells on the human retina give us an amazing visual resolution, but they also require a prodigious amount of blood to keep them going. This blood is what gives the retina its red color.

Most people with color blindness can see almost all colors. They are typically only blind to a few colors. Furthermore, they are not completely blind to those colors, but are only partially blind. The human eye contains three types of color detecting cells: red-detecting cones, green-detecting cones, and blue-detecting cones. Each cone cell can detect many colors in addition to its main color. For instance, the cone cells in the eye that can see red light can also see orange and yellow. The red cone cells just see red the best, and that is why they are called the red cones. Similarly, the green cones can also see orange, yellow and blue. This overlap is what allows humans to see so many different colors. Humans can see the color yellow, for instance, even though there are no yellow receptors, because of this overlap. When you look at a yellow flower, the yellow light stimulates the red and green cells in your eyes, and your brain interprets a little bit of red plus a little bit of green as yellow.

All parts of the tongue can taste every flavor. The tongue, and indeed the sides of the mouth, the epiglottis and other tissues are all covered with taste buds. Each taste bud contains many taste cells that can taste different flavors. According to the textbook "Neuroscience" edited by Dale Purves, this misconception dates back to the research of German scientist D. P. Hanig, published in 1901. Hanig simply noted down the subjective remarks of volunteers describing where they tasted a flavor. Unable to find a clear delineation of regions, Hanig recorded that certain areas of the tongue were slightly more sensitive to flavors than others based on statistically incomplete data. Other researchers interpreted his publication to mean that only certain parts of the tongue can taste certain flavors. Despite the ease of anybody disproving this theory by simply placing a pinch of salt at the tip of their tongue (which supposedly can only taste sweet), this misconception has lingered for a century. Perhaps the reason for the inability of this myth to die is the fact that a picture of a tongue with different parts colored and labeled makes for such an eye-catching image in science books. In 1905, Einstein published his landmark paper on special relativity. It is amazing that around the same time mankind was unraveling the mysteries of time travel, we were misunderstanding science that was literally on the tip of our tongue. More amazing is that this misunderstanding has persisted for over a century.

The brains of humans are not the biggest compared to all other animals. The average human brain has a mass of about 1 kg. In contrast, the brain of a sperm whale has a mass of 8 kg and that of an elephant has a mass of 5 kg. You may be tempted to think that bigger brains means smarter and that because humans are the smartest animals, we must have the biggest brains. But biology does not work that way. When an animal has a larger overall size, all of its organs must be generally bigger just to keep it alive. A sperm whale weighs 35 to 45 metric tons and stretches about 15 meters long. With so much biological tissue to take care of, the sperm whale needs a giant heart to keep blood pumping to all this tissue, giant lungs to provide oxygen to all this tissue, and a giant brain to coordinate it all. The sperm whale needs a giant brain not because it is intelligent, but because it has so much low-level functions to carry out with such a huge body.

Bats are not blind and can in fact see quite well using their eyes. While most bats do have advanced ears that give them a form of vision in the dark known as echolocation, these good ears does not require them to have bad eyes. Bats use their good hearing to find food in the dark of night, and their good eyes to find food during the light of day. The vision of bats is tuned to low-light conditions such as is present during dawn and dusk. While some bats may not have as good color vision as humans, their overall vision may be better than humans during dawn and dusk.

From one point of view, the original cell you came from (the fertilized egg cell) was destroyed long before your body was formed. From another point of view, every cell in your body is the original. In either case, there is not just one original cell sitting in your elbow or toe that can be identified as the ancestor of all your other cells.

Birds do not have teeth. Without teeth, a bird cannot chew its food down to bits in its mouth like humans do. As detailed in the textbook Ornithology by Frank B. Gill, birds must instead rely on the muscular stomach-like pouch called the gizzard to crush down their food. Many species swallow stones and grit to aid in digestion. These stones remain in the gizzard and crush the food as the gizzard contracts. From a functional perspective, gizzard stones in birds are the equivalent of teeth in humans. When a gizzard stone becomes too smooth to do its job, the bird regurgitates the stone or passes the stone down and out through its digestive tract. Species that do not swallow stones are able to use the sheer muscle power of their gizzards to grind down their food. Birds do not have teeth because the teeth and the jaw bone to support them are too heavy for efficient flight. Many birds have a series of notches in their beak or spikes on the inside of their beak or tongue. These notches and spikes are not true teeth as they are not used to crush down their food. Instead, these features are used to get a good grip on the prey so that it does not escape. In ancient evolutionary history, there were birds with true teeth. Known as odontornithes, these animals are no longer alive today.

Humans have never stopped evolving and continue to do so today. Evolution is a slow process that takes many generations of reproduction to become evident. Because humans take so long to reproduce, it takes hundreds to thousands of years for changes in humans to become evident. We simply don't notice the evolution of humans from day to day because it is happening so slowly. But creatures that reproduce more quickly also evolve more quickly. For instance, bacteria can reproduce within 20 minutes, so their evolution can be watched by scientists over the course of a few days. All creatures are always evolving. There is no way to stop evolution.

No chemicals can make human tissue regenerate in seconds. Biological tissue is composed mainly of a large collection of cells sitting in a scaffolding of proteins and sugar chains (the extracellular matrix) and bathed in fluids that carry various chemicals between the cells. The regeneration of tissue mainly involves the fabrication of the extracellular matrix, which is secreted by cells, and the creation of new cells by way of cell division. Therefore, the rate at which tissue regenerates is mainly limited by how fast one cell can divide into two new, fully-functional cells that then become mature enough to divide again. This cell reproduction time depends on the type of cell, but for humans the shortest duration of a single cell cycle is about one day. In order to generate a decent amount of tissue, several cell cycles will be needed, so the total time to regenerate tissue is at the very best a few days. This number is an absolute minimum. In most cases, it will take far longer for a human to regenerate a significant amount of tissue; from weeks to months. Furthermore, if the need to regenerate is caused by acute damage to the tissue, the body may respond by forming a scar rather than regenerating the tissue. Certain types of human tissue simply can't regenerate on their own in response to significant injury. Even if we could apply chemicals that force the tissue to regenerate as fast as possible (but still remain as somewhat normal human cells), the best we can do is to have tissue regenerate in few day, not in a few seconds.

No, ionizing radiation is only harmful to an organism as a whole when its amount gets too high. We are constantly bombarded with very small amounts of ionizing radiation that occur naturally, and we get along just fine with our lives without being seriously harmed by this radiation. There are trace amounts of naturally-occurring radioactive atoms in the air, in the rocks, in our food, and inside our bodies. When these atoms radioactively decay, they emit ionizing radiation. By its nature of being ionizing, such radiation can damage individual molecules, even at low intensity. But if the amount of ionizing radiation exposure is very low, our bodies can handle a few damaged molecules without any problem, so that there is no net harm done to our bodies.