Little green yard lizards have necks that expand and turn rosy red when they are seeking a mate. 'Come hither!' the bright splash of swelling color seems to say. Fireflies (a.k.a. lightning bugs) have  bodies that blink brightly in the night. 'Here I am!' they seem to say. People have faces that turn rosy with interest and shyness. The pupils of their eyes dilate. 'Umm. Do you like me?' their faces seem to say. Frogs croak over and over: 'Come find me! I'm at the pond!'