What is the red thing on a chicken?

The red thing on a chicken is typically called a comb. It is a fleshy, elevated growth on top of the chicken's head that helps regulate the bird's body temperature. The comb is made up of blood vessels and can change in color and size depending on factors such as the chicken's health and environment.

In addition to assisting with temperature regulation, the comb also plays a role in communication and social hierarchy within a flock. Different breeds of chickens have different types of combs, ranging from small and smooth to large and floppy. Some common types of combs include single comb, rose comb, pea comb, and walnut comb.