Arboreal locomotion small branches, as they may wrap too far around and prick the animal's own paw. Adhesion is an alternative to claws, which works best on smooth surfaces. Wet adhesion is common in tree frogs and arboreal salamanders, and functions either by suction or by capillary adhesion. Dry adhesion is best typified by the specialized toes of geckos, which use van der Waals forces to adhere to many substrates, even glass. Frictional gripping is used by primates, relying upon hairless fingertips. Squeezing the branch between the fingertips generates a frictional force that holds the animal's hand to the branch. However, this
Blindness in animals Blindness in animals Visual perception animals play an important role in the animal kingdom, most importantly for the identification of food sources and avoidance of predators. For this reason, blindness in animals is a unique topic of study. In general, nocturnal or subterranean animals have less interest in the visual world, and depend on other sensory modalities. Visual capacity is a continuum, with humans falling somewhere in the center. Animals that live only in caves, called troglobites (meaning 'cave dwellers'), are adapted to life in the dark. Many such species are blind or have poor vision. Blindness at birth serves