Erythrism is usually seen in some animals, like birds, cats or dogs. It's when the fur or feathers of the animal take on a reddish color, instead of their natural color. It's caused by a genetic difference that affects the animal's ability to make a certain type of color pigment. This means that the pigment is not made correctly, and it's replaced by a reddish version instead. Erythrism is fun and interesting to look at, but it can also cause health problems for the animals.