Green geckos are sometimes heard before seen. As night turns dark a staccato call of "Geck-o! Geck-o!" may be heard sharply emanating from the tree or the building. When they are spotted, these nimble lizards can be heavily patterned with spots, squares and dashes in black, yellow, brown and white. While females are green, the males are grey with white and brown splotches. The inside of the mouth, which is revealed in a threat display in some species, is deep blue, orange, pink or red. The broad fleshy tongue, which has a major function in cleaning the transparent scales which cover the eyes, is also brightly colored; depending on the species it is red, orange, pink, yellow or black. The ears of geckos appear as small openings on the side of the head behind the eyes, and the eardrum is visible a short distance inside this opening. Geckos evolved very similar hairy adhesive toe pads that help them adhere to and navigate vertical and inverted surfaces.