If you were a cell, how would you say hello to your neighbor? Well, okay, you probably wouldn't be saying hello. (Maybe something more like "Divide now!" or "Become a skin cell!") Whatever you might be saying, however, chances are you'd be saying it in the form of chemical signals. Learn more about the types of signaling molecules cells use, the receptors that perceive them, and the types of changes they produce inside of the cell.