Cilia are tiny, hair-like structures that extend from the surface of many cells. They play a crucial role in movement and sensing the environment. For example, in the human body, cilia help move mucus out of the lungs, keeping our airways clear. They can also be found in single-celled organisms like Paramecium, where they help the organism swim through water. In addition to movement, cilia are important for communication between cells. They can detect signals from other cells and help coordinate activities. This is especially important in the development of embryos and in the functioning of organs like the brain and heart.